Skip to Main Navigation
Skip to Page Content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Share This:
https://ntp.niehs.nih.gov/go/4534

TDMS Study 05185-04 Pathology Tables


                                     INCIDENCE RATES OF NONNEOPLASTIC LESIONS BY ANATOMIC SITE (a)
                                                       ISOBUTYL NITRITE (IBN)


NTP Experiment-Test: 05185-04                                                                                     Report: PEIRPT03
Study Type: CHRONIC                                                                                               Date: 05/20/95
Route: RESPIRATORY EXPOSURE WHOLE BODY                                                                            Time: 11:28:48




       Facility:  I. I. T. Research Institute

       Chemical CAS #:  542-56-3

       Lock Date:  08/20/92

       Cage Range:  All

       Reasons For Removal:    All

       Removal Date Range:     All

       Treatment Groups:       Include All
































a  Number of animals examined microscopically at site and number of animals with lesion

                                                             Page   1

NTP Experiment-Test: 05185-04         INCIDENCE RATES OF NONNEOPLASTIC LESIONS BY ANATOMIC SITE (a)               Report: PEIRPT03
Study Type: CHRONIC                                       ISOBUTYL NITRITE (IBN)                                  Date: 05/20/95  
Route: RESPIRATORY EXPOSURE WHOLE BODY                                                                            Time: 11:28:48  
____________________________________________________________________________________________________________________________________
         B6C3F1 MICE FEMALE                        CONTROL      37.5 PPM     75 PPM       150 PPM                                   
                                                                                                                                    
____________________________________________________________________________________________________________________________________
DISPOSITION SUMMARY                                                                                                                 
  Animals Initially In Study                          60           60           60           60                                     
  Scheduled Sacrifice                                  9            9            9           10                                     
  Early Deaths                                                                                                                      
    Natural Death                                     16            6            8           10                                     
    Moribund Sacrifice                                 3            3            6            2                                     
    Accidently Killed                                                                         1                                     
  Survivors                                                                                                                         
    Terminal Sacrifice                                32           42           36           37                                     
  Other                                                                          1                                                  
  Animals Examined Microscopically                    60           60           59           60                                     
____________________________________________________________________________________________________________________________________
                                                                                                                                    
 ALIMENTARY SYSTEM                                                                                                                  
                                                                                                                                    
   Gallbladder                                        (55)         (55)         (54)         (51)                                   
      Dilatation                                                                              1 (2%)                                
      Inflammation, Chronic                                                      1 (2%)       1 (2%)                                
   Intestine Large, Rectum                            (57)         (60)         (59)         (57)                                   
      Dilatation                                                                 1 (2%)                                             
   Intestine Large, Cecum                             (57)         (58)         (59)         (55)                                   
      Dilatation                                                                 1 (2%)                                             
      Hyperplasia, Lymphoid                                                      1 (2%)                                             
   Intestine Small, Duodenum                          (51)         (59)         (58)         (52)                                   
      Ectopic Tissue                                                1 (2%)                                                          
      Proliferation Connective Tissue                               1 (2%)                                                          
   Intestine Small, Jejunum                           (53)         (59)         (56)         (55)                                   
      Hyperplasia, Lymphoid                                         1 (2%)                                                          
      Proliferation Connective Tissue                               1 (2%)                                                          
      Serosa, Inflammation, Chronic Active                          1 (2%)                                                          
   Intestine Small, Ileum                             (53)         (57)         (59)         (54)                                   
      Dilatation                                                                 1 (2%)                                             
   Liver                                              (60)         (60)         (59)         (60)                                   
      Angiectasis                                                                             1 (2%)                                
      Basophilic Focus                                 2 (3%)                                 1 (2%)                                
      Clear Cell Focus                                              1 (2%)       2 (3%)       1 (2%)                                
      Cytologic Alterations                            2 (3%)       1 (2%)       1 (2%)                                             
      Eosinophilic Focus                               1 (2%)       2 (3%)                                                          
      Fatty Change, Diffuse                            1 (2%)                                                                       
      Fibrosis                                                                   1 (2%)                                             
      Hematopoietic Cell Proliferation                 1 (2%)       1 (2%)       1 (2%)                                             
      Hemorrhage                                                                              1 (2%)                                
      Hyperplasia                                                                             2 (3%)                                
      Infarct                                                                    1 (2%)       1 (2%)                                
      Inflammation, Chronic                           11 (18%)      7 (12%)      6 (10%)      7 (12%)                               
a  Number of animals examined microscopically at site and number of animals with lesion                                             
                                                             Page    2                                                              
NTP Experiment-Test: 05185-04         INCIDENCE RATES OF NONNEOPLASTIC LESIONS BY ANATOMIC SITE (a)               Report: PEIRPT03
Study Type: CHRONIC                                       ISOBUTYL NITRITE (IBN)                                  Date: 05/20/95  
Route: RESPIRATORY EXPOSURE WHOLE BODY                                                                            Time: 11:28:48  
____________________________________________________________________________________________________________________________________
         B6C3F1 MICE FEMALE                        CONTROL      37.5 PPM     75 PPM       150 PPM                                   
                                                                                                                                    
____________________________________________________________________________________________________________________________________
                                                                                                                                    
ALIMENTARY SYSTEM - CONT                                                                                                            
      Inflammation, Chronic Active                     2 (3%)       2 (3%)       4 (7%)                                             
      Mitotic Alteration                                            1 (2%)                                                          
      Mixed Cell Focus                                 3 (5%)       1 (2%)       1 (2%)       2 (3%)                                
      Necrosis                                         1 (2%)       2 (3%)       2 (3%)       1 (2%)                                
      Pigmentation                                                                            1 (2%)                                
      Proliferation Connective Tissue                               1 (2%)                                                          
      Fat, Necrosis                                    1 (2%)                                                                       
      Hepatocyte, Necrosis                             1 (2%)       1 (2%)       1 (2%)                                             
      Periportal, Fatty Change                         1 (2%)                    1 (2%)                                             
      Periportal, Hypertrophy                                       1 (2%)                                                          
   Mesentery                                          (7)          (4)          (3)          (2)                                    
      Cyst                                                          1 (25%)                                                         
      Proliferation Connective Tissue                               1 (25%)                                                         
      Artery, Inflammation, Chronic                    1 (14%)                                                                      
      Fat, Necrosis                                    5 (71%)      4 (100%)     2 (67%)      2 (100%)                              
   Pancreas                                           (60)         (60)         (59)         (60)                                   
      Fibrosis                                                      1 (2%)                                                          
      Inflammation, Chronic                            4 (7%)                                 3 (5%)                                
      Inflammation, Chronic Active                                  1 (2%)                                                          
      Acinus, Atrophy                                  1 (2%)       2 (3%)       3 (5%)       2 (3%)                                
      Duct, Dilatation                                              1 (2%)       1 (2%)                                             
   Salivary Glands                                    (60)         (60)         (59)         (60)                                   
      Atrophy                                                                    1 (2%)                                             
      Hemorrhage                                                                              1 (2%)                                
      Inflammation, Chronic                           49 (82%)     44 (73%)     33 (56%)     32 (53%)                               
      Inflammation, Chronic Active                                  1 (2%)                                                          
   Stomach, Forestomach                               (60)         (60)         (59)         (59)                                   
      Angiectasis                                                                             1 (2%)                                
      Developmental Malformation                                                              1 (2%)                                
      Proliferation Connective Tissue                               1 (2%)                                                          
      Ulcer                                                                      1 (2%)                                             
   Stomach, Glandular                                 (60)         (60)         (59)         (59)                                   
      Proliferation Connective Tissue                               1 (2%)                                                          
____________________________________________________________________________________________________________________________________
                                                                                                                                    
 CARDIOVASCULAR SYSTEM                                                                                                              
                                                                                                                                    
   Heart                                              (60)         (60)         (59)         (60)                                   
      Infiltration Cellular                            1 (2%)                                                                       
      Inflammation, Chronic                            1 (2%)                                                                       
      Thrombosis                                       1 (2%)                    1 (2%)                                             
      Artery, Hypertrophy                                                        1 (2%)                                             
      Artery, Inflammation, Chronic                    1 (2%)       1 (2%)                    1 (2%)                                
____________________________________________________________________________________________________________________________________
                                                                                                                                    
a  Number of animals examined microscopically at site and number of animals with lesion                                             
                                                             Page    3                                                              
NTP Experiment-Test: 05185-04         INCIDENCE RATES OF NONNEOPLASTIC LESIONS BY ANATOMIC SITE (a)               Report: PEIRPT03
Study Type: CHRONIC                                       ISOBUTYL NITRITE (IBN)                                  Date: 05/20/95  
Route: RESPIRATORY EXPOSURE WHOLE BODY                                                                            Time: 11:28:48  
____________________________________________________________________________________________________________________________________
         B6C3F1 MICE FEMALE                        CONTROL      37.5 PPM     75 PPM       150 PPM                                   
                                                                                                                                    
____________________________________________________________________________________________________________________________________
                                                                                                                                    
 ENDOCRINE SYSTEM                                                                                                                   
                                                                                                                                    
   Adrenal Cortex                                     (59)         (60)         (59)         (59)                                   
      Cyst                                                                       3 (5%)                                             
      Hyperplasia, Focal                                            2 (3%)                                                          
      Hypertrophy, Focal                                            1 (2%)       2 (3%)                                             
      Subcapsular, Hyperplasia                        56 (95%)     56 (93%)     54 (92%)     53 (90%)                               
   Adrenal Medulla                                    (55)         (58)         (54)         (57)                                   
      Hyperplasia, Focal                                            2 (3%)       1 (2%)                                             
   Islets, Pancreatic                                 (2)          (2)          (3)          (3)                                    
      Hyperplasia, Focal                               2 (100%)     1 (50%)      3 (100%)     2 (67%)                               
   Pituitary Gland                                    (56)         (56)         (59)         (57)                                   
      Cyst                                                                       1 (2%)                                             
      Pars Distalis, Angiectasis                       1 (2%)                    1 (2%)       2 (4%)                                
      Pars Distalis, Cyst                              1 (2%)       1 (2%)       1 (2%)       2 (4%)                                
      Pars Distalis, Hemorrhage                        1 (2%)                                                                       
      Pars Distalis, Hyperplasia                      10 (18%)     12 (21%)     12 (20%)      7 (12%)                               
      Pars Distalis, Hyperplasia, Focal                             1 (2%)                                                          
   Thyroid Gland                                      (60)         (60)         (59)         (60)                                   
      Ectopic Thymus                                                             1 (2%)                                             
      Infiltration Cellular, Lymphocyte                             1 (2%)                                                          
      Inflammation, Chronic                                                      3 (5%)                                             
      Follicle, Cyst                                   1 (2%)       5 (8%)       4 (7%)                                             
      Follicular Cell, Hyperplasia, Diffuse            1 (2%)                    1 (2%)                                             
      Follicular Cell, Hyperplasia, Focal              5 (8%)       9 (15%)      7 (12%)      5 (8%)                                
____________________________________________________________________________________________________________________________________
                                                                                                                                    
 GENERAL BODY SYSTEM                                                                                                                
                                                                                                                                    
   None                                                                                                                             
____________________________________________________________________________________________________________________________________
                                                                                                                                    
 GENITAL SYSTEM                                                                                                                     
                                                                                                                                    
   Clitoral Gland                                                  (1)          (2)          (5)                                    
      Dilatation                                                    1 (100%)     1 (50%)      1 (20%)                               
      Pigmentation                                                                            3 (60%)                               
   Ovary                                              (58)         (59)         (55)         (59)                                   
      Angiectasis                                                                             1 (2%)                                
      Cyst                                            10 (17%)     15 (25%)     10 (18%)     13 (22%)                               
      Hemorrhage                                                                              1 (2%)                                
      Infiltration Cellular, Lymphocyte                1 (2%)                                 1 (2%)                                
      Interstitium, Hyperplasia                        1 (2%)                                                                       
   Uterus                                             (60)         (60)         (58)         (59)                                   
      Angiectasis                                      2 (3%)                                 1 (2%)                                
      Developmental Malformation                                                 1 (2%)                                             
      Dilatation                                                    1 (2%)                                                          
      Hemorrhage                                       1 (2%)                                                                       
a  Number of animals examined microscopically at site and number of animals with lesion                                             
                                                             Page    4                                                              
NTP Experiment-Test: 05185-04         INCIDENCE RATES OF NONNEOPLASTIC LESIONS BY ANATOMIC SITE (a)               Report: PEIRPT03
Study Type: CHRONIC                                       ISOBUTYL NITRITE (IBN)                                  Date: 05/20/95  
Route: RESPIRATORY EXPOSURE WHOLE BODY                                                                            Time: 11:28:48  
____________________________________________________________________________________________________________________________________
         B6C3F1 MICE FEMALE                        CONTROL      37.5 PPM     75 PPM       150 PPM                                   
                                                                                                                                    
____________________________________________________________________________________________________________________________________
                                                                                                                                    
GENITAL SYSTEM - CONT                                                                                                               
      Hyperplasia                                                   1 (2%)                                                          
      Hyperplasia, Cystic                             49 (82%)     51 (85%)     50 (86%)     54 (92%)                               
      Inflammation, Chronic Active                                               1 (2%)                                             
____________________________________________________________________________________________________________________________________
                                                                                                                                    
 HEMATOPOIETIC SYSTEM                                                                                                               
                                                                                                                                    
   Bone Marrow                                        (60)         (60)         (59)         (60)                                   
      Atrophy                                                       1 (2%)                                                          
      Degeneration, Fatty                              1 (2%)                                                                       
      Myeloid Cell, Hyperplasia                                     1 (2%)       3 (5%)                                             
   Lymph Node                                         (4)          (5)          (8)          (6)                                    
      Hyperplasia, Lymphoid                                         1 (20%)                                                         
      Pigmentation                                                  1 (20%)                                                         
      Iliac, Hemorrhage                                                          1 (13%)                                            
      Iliac, Hyperplasia, Lymphoid                                  1 (20%)                                                         
      Iliac, Inflammation, Chronic Active                                        1 (13%)                                            
      Iliac, Pigmentation                                                                     1 (17%)                               
      Inguinal, Pigmentation                                                                  1 (17%)                               
      Lumbar, Angiectasis                                                        1 (13%)                                            
      Lumbar, Hemorrhage                                                         1 (13%)                                            
      Lumbar, Hyperplasia, Lymphoid                                                           1 (17%)                               
      Pancreatic, Hyperplasia, Lymphoid                             1 (20%)                                                         
      Renal, Hemorrhage                                                          1 (13%)                                            
   Lymph Node, Bronchial                              (28)         (42)         (40)         (38)                                   
      Hemorrhage                                                    1 (2%)       1 (3%)                                             
      Hyperplasia, Lymphoid                            1 (4%)       4 (10%)                                                         
   Lymph Node, Mandibular                             (58)         (57)         (57)         (55)                                   
      Hemorrhage                                                    1 (2%)       2 (4%)       1 (2%)                                
      Hyperplasia, Lymphoid                            2 (3%)       1 (2%)       2 (4%)       1 (2%)                                
      Inflammation, Chronic Active                     1 (2%)                                                                       
   Lymph Node, Mesenteric                             (60)         (59)         (58)         (55)                                   
      Angiectasis                                                                             1 (2%)                                
      Hematopoietic Cell Proliferation                 1 (2%)                                                                       
      Hemorrhage                                       1 (2%)                    1 (2%)                                             
      Hyperplasia, Lymphoid                                         1 (2%)       1 (2%)       1 (2%)                                
      Hyperplasia, Plasma Cell                                      1 (2%)                                                          
      Inflammation, Chronic Active                     1 (2%)                                                                       
   Lymph Node, Mediastinal                            (58)         (51)         (52)         (53)                                   
      Hyperplasia, Lymphoid                            6 (10%)      4 (8%)       3 (6%)       3 (6%)                                
      Inflammation, Chronic Active                                               1 (2%)                                             
   Spleen                                             (60)         (60)         (59)         (59)                                   
      Angiectasis                                                   1 (2%)                                                          
      Atrophy                                          1 (2%)                                                                       
      Fibrosis                                         1 (2%)                                                                       
      Hematopoietic Cell Proliferation                54 (90%)     49 (82%)     54 (92%)     54 (92%)                               
      Hyperplasia, Lymphoid                            6 (10%)      7 (12%)      6 (10%)      3 (5%)                                
a  Number of animals examined microscopically at site and number of animals with lesion                                             
                                                             Page    5                                                              
NTP Experiment-Test: 05185-04         INCIDENCE RATES OF NONNEOPLASTIC LESIONS BY ANATOMIC SITE (a)               Report: PEIRPT03
Study Type: CHRONIC                                       ISOBUTYL NITRITE (IBN)                                  Date: 05/20/95  
Route: RESPIRATORY EXPOSURE WHOLE BODY                                                                            Time: 11:28:48  
____________________________________________________________________________________________________________________________________
         B6C3F1 MICE FEMALE                        CONTROL      37.5 PPM     75 PPM       150 PPM                                   
                                                                                                                                    
____________________________________________________________________________________________________________________________________
                                                                                                                                    
HEMATOPOIETIC SYSTEM - CONT                                                                                                         
      Pigmentation, Hemosiderin                       54 (90%)     52 (87%)     46 (78%)     57 (97%)                               
      Proliferation Connective Tissue                               1 (2%)                                                          
   Thymus                                             (56)         (56)         (57)         (51)                                   
      Atrophy                                         11 (20%)      2 (4%)       5 (9%)       6 (12%)                               
      Ectopic Parathyroid Gland                                                               1 (2%)                                
      Hemorrhage                                                                 1 (2%)                                             
      Hyperplasia, Lymphoid                            5 (9%)      10 (18%)      6 (11%)      2 (4%)                                
____________________________________________________________________________________________________________________________________
                                                                                                                                    
 INTEGUMENTARY SYSTEM                                                                                                               
                                                                                                                                    
   Mammary Gland                                      (58)         (60)         (59)         (60)                                   
      Dilatation                                                                 1 (2%)       2 (3%)                                
      Hyperplasia                                      2 (3%)       1 (2%)       1 (2%)       2 (3%)                                
   Skin                                               (60)         (60)         (59)         (60)                                   
      Inflammation, Chronic                            6 (10%)                                4 (7%)                                
      Inflammation, Chronic Active                                  4 (7%)       2 (3%)                                             
      Ulcer                                                         1 (2%)                                                          
      Epithelium, Hyperplasia                          1 (2%)       2 (3%)       2 (3%)                                             
      Sebaceous Gland, Hyperplasia, Focal                                        1 (2%)                                             
____________________________________________________________________________________________________________________________________
                                                                                                                                    
 MUSCULOSKELETAL SYSTEM                                                                                                             
                                                                                                                                    
   Bone                                               (60)         (60)         (59)         (60)                                   
      Developmental Malformation                                    1 (2%)                                                          
      Dysplasia                                       24 (40%)     18 (30%)     25 (42%)     28 (47%)                               
      Hyperostosis                                                  1 (2%)                                                          
      Maxilla, Fracture                                                                       1 (2%)                                
   Skeletal Muscle                                                 (3)          (1)          (1)                                    
      Hemorrhage                                                                 1 (100%)                                           
      Proliferation Connective Tissue                               1 (33%)                                                         
____________________________________________________________________________________________________________________________________
                                                                                                                                    
 NERVOUS SYSTEM                                                                                                                     
                                                                                                                                    
   Brain                                              (59)         (60)         (59)         (60)                                   
      Compression                                      1 (2%)       1 (2%)       4 (7%)       2 (3%)                                
      Hemorrhage                                                                 2 (3%)       1 (2%)                                
      Mineralization                                  45 (76%)     26 (43%)     31 (53%)     27 (45%)                               
      Meninges, Inflammation, Chronic Active                                                  1 (2%)                                
   Spinal Cord                                                                               (1)                                    
      Inflammation, Chronic                                                                   1 (100%)                              
____________________________________________________________________________________________________________________________________
                                                                                                                                    
a  Number of animals examined microscopically at site and number of animals with lesion                                             
                                                             Page    6                                                              
NTP Experiment-Test: 05185-04         INCIDENCE RATES OF NONNEOPLASTIC LESIONS BY ANATOMIC SITE (a)               Report: PEIRPT03
Study Type: CHRONIC                                       ISOBUTYL NITRITE (IBN)                                  Date: 05/20/95  
Route: RESPIRATORY EXPOSURE WHOLE BODY                                                                            Time: 11:28:48  
____________________________________________________________________________________________________________________________________
         B6C3F1 MICE FEMALE                        CONTROL      37.5 PPM     75 PPM       150 PPM                                   
                                                                                                                                    
____________________________________________________________________________________________________________________________________
                                                                                                                                    
 RESPIRATORY SYSTEM                                                                                                                 
                                                                                                                                    
   Larynx                                             (60)         (58)         (59)         (59)                                   
      Artery, Inflammation, Chronic                                                           1 (2%)                                
   Lung                                               (60)         (60)         (59)         (60)                                   
      Infiltration Cellular, Lymphocyte               28 (47%)     14 (23%)     11 (19%)     23 (38%)                               
      Inflammation, Chronic Active                     3 (5%)       3 (5%)       1 (2%)                                             
      Leukocytosis                                     1 (2%)                                                                       
      Alveolar Epithelium, Hyperplasia, Focal                       2 (3%)      10 (17%)      8 (13%)                               
      Alveolus, Infiltration Cellular, Histiocyte                   1 (2%)       1 (2%)       2 (3%)                                
      Artery, Inflammation, Chronic                                 1 (2%)                                                          
      Fat, Mediastinum, Necrosis                                    1 (2%)                                                          
   Nose                                               (60)         (60)         (59)         (60)                                   
      Exudate                                          1 (2%)                                                                       
      Exudate, Serous                                  1 (2%)       1 (2%)       2 (3%)      23 (38%)                               
      Inflammation, Chronic Active                     6 (10%)     10 (17%)     12 (20%)     12 (20%)                               
      Olfactory Epithelium, Atrophy                                              1 (2%)      16 (27%)                               
      Olfactory Epithelium, Degeneration, Hyaline      4 (7%)       3 (5%)       5 (8%)       3 (5%)                                
      Olfactory Epithelium, Metaplasia                              6 (10%)      2 (3%)       2 (3%)                                
      Olfactory Epithelium, Metaplasia, Squamous                    1 (2%)                    1 (2%)                                
      Respiratory Epithelium, Degeneration, Hyaline   19 (32%)     26 (43%)     14 (24%)     19 (32%)                               
      Respiratory Epithelium, Hyperplasia              6 (10%)      3 (5%)       4 (7%)       1 (2%)                                
      Respiratory Epithelium, Metaplasia, Squamous     4 (7%)       5 (8%)                    6 (10%)                               
      Respiratory Epithelium, Ulcer                    3 (5%)       4 (7%)       3 (5%)       3 (5%)                                
____________________________________________________________________________________________________________________________________
                                                                                                                                    
 SPECIAL SENSES SYSTEM                                                                                                              
                                                                                                                                    
   Eye                                                                                       (1)                                    
      Phthisis Bulbi                                                                          1 (100%)                              
____________________________________________________________________________________________________________________________________
                                                                                                                                    
 URINARY SYSTEM                                                                                                                     
                                                                                                                                    
   Kidney                                             (60)         (60)         (59)         (60)                                   
      Amyloid Deposition                               1 (2%)                                                                       
      Cyst                                             1 (2%)                                                                       
      Glomerulosclerosis                                                                      1 (2%)                                
      Hydronephrosis                                   1 (2%)                    1 (2%)                                             
      Infarct                                                                                 1 (2%)                                
      Infiltration Cellular, Lymphocyte               35 (58%)     19 (32%)     19 (32%)     31 (52%)                               
      Nephropathy                                                   2 (3%)       1 (2%)                                             
      Renal Tubule, Degeneration, Hyaline              1 (2%)                                                                       
      Renal Tubule, Dilatation                         2 (3%)       1 (2%)       2 (3%)       1 (2%)                                
      Renal Tubule, Hyperplasia, Focal                 1 (2%)                                 1 (2%)                                
      Renal Tubule, Pigmentation                                    1 (2%)                                                          
      Renal Tubule, Regeneration                                    1 (2%)                    1 (2%)                                
   Urinary Bladder                                    (58)         (59)         (57)         (57)                                   
a  Number of animals examined microscopically at site and number of animals with lesion                                             
                                                             Page    7                                                              
NTP Experiment-Test: 05185-04         INCIDENCE RATES OF NONNEOPLASTIC LESIONS BY ANATOMIC SITE (a)               Report: PEIRPT03
Study Type: CHRONIC                                       ISOBUTYL NITRITE (IBN)                                  Date: 05/20/95  
Route: RESPIRATORY EXPOSURE WHOLE BODY                                                                            Time: 11:28:48  
____________________________________________________________________________________________________________________________________
         B6C3F1 MICE FEMALE                        CONTROL      37.5 PPM     75 PPM       150 PPM                                   
                                                                                                                                    
____________________________________________________________________________________________________________________________________
                                                                                                                                    
URINARY SYSTEM - CONT                                                                                                               
      Dilatation                                                    1 (2%)                                                          
      Infiltration Cellular, Lymphocyte               38 (66%)     40 (68%)     24 (42%)     34 (60%)                               
                                                                                                                                    
a  Number of animals examined microscopically at site and number of animals with lesion                                             
                                                             Page    8                                                              
NTP Experiment-Test: 05185-04         INCIDENCE RATES OF NONNEOPLASTIC LESIONS BY ANATOMIC SITE (a)               Report: PEIRPT03
Study Type: CHRONIC                                       ISOBUTYL NITRITE (IBN)                                  Date: 05/20/95  
Route: RESPIRATORY EXPOSURE WHOLE BODY                                                                            Time: 11:28:48  
____________________________________________________________________________________________________________________________________
         B6C3F1 MICE MALE                          CONTROL      37.5 PPM     75 PPM       150 PPM                                   
                                                                                                                                    
____________________________________________________________________________________________________________________________________
DISPOSITION SUMMARY                                                                                                                 
  Animals Initially In Study                          60           60           60           60                                     
  Scheduled Sacrifice                                 10           10           10            7                                     
  Early Deaths                                                                                                                      
    Natural Death                                     10            8           11           17                                     
    Accidently Killed                                  2                                      2                                     
    Moribund Sacrifice                                 1            7            4            4                                     
  Survivors                                                                                                                         
    Terminal Sacrifice                                37           35           35           30                                     
  Animals Examined Microscopically                    60           60           60           60                                     
____________________________________________________________________________________________________________________________________
                                                                                                                                    
 ALIMENTARY SYSTEM                                                                                                                  
                                                                                                                                    
   Gallbladder                                        (51)         (50)         (51)         (53)                                   
      Inflammation, Chronic Active                                                            1 (2%)                                
   Intestine Large, Cecum                             (54)         (55)         (55)         (50)                                   
      Hyperplasia, Lymphoid                                         2 (4%)                                                          
   Intestine Small, Duodenum                          (53)         (55)         (55)         (50)                                   
      Proliferation Connective Tissue                               1 (2%)                                                          
   Intestine Small, Jejunum                           (52)         (55)         (56)         (50)                                   
      Hyperplasia, Lymphoid                                         1 (2%)                                                          
      Inflammation, Chronic Active                                  1 (2%)                                                          
   Liver                                              (60)         (60)         (60)         (60)                                   
      Abscess                                                                                 1 (2%)                                
      Angiectasis                                      1 (2%)       1 (2%)                                                          
      Basophilic Focus                                 3 (5%)       2 (3%)       2 (3%)       2 (3%)                                
      Clear Cell Focus                                 2 (3%)       3 (5%)       3 (5%)                                             
      Cytologic Alterations                            3 (5%)                    2 (3%)       2 (3%)                                
      Developmental Malformation                                    1 (2%)                                                          
      Eosinophilic Focus                               1 (2%)                    1 (2%)                                             
      Fatty Change, Focal                              1 (2%)                    1 (2%)                                             
      Hematopoietic Cell Proliferation                              1 (2%)       1 (2%)       1 (2%)                                
      Hyperplasia                                                                             1 (2%)                                
      Infarct                                          2 (3%)       2 (3%)       3 (5%)       2 (3%)                                
      Inflammation, Chronic                                         1 (2%)                    5 (8%)                                
      Inflammation, Chronic Active                                  1 (2%)       1 (2%)                                             
      Mixed Cell Focus                                              5 (8%)       1 (2%)       1 (2%)                                
      Necrosis                                         1 (2%)       3 (5%)       3 (5%)       4 (7%)                                
      Proliferation Connective Tissue                               1 (2%)                    1 (2%)                                
      Syncytial Alteration                            12 (20%)     14 (23%)     16 (27%)     11 (18%)                               
      Vacuolization Cytoplasmic                        1 (2%)                                                                       
      Bile Duct, Cyst                                                            2 (3%)                                             
      Bile Duct, Hyperplasia                                                     1 (2%)       1 (2%)                                
      Centrilobular, Fatty Change                      5 (8%)       6 (10%)      4 (7%)       1 (2%)                                
a  Number of animals examined microscopically at site and number of animals with lesion                                             
                                                             Page    9                                                              
NTP Experiment-Test: 05185-04         INCIDENCE RATES OF NONNEOPLASTIC LESIONS BY ANATOMIC SITE (a)               Report: PEIRPT03
Study Type: CHRONIC                                       ISOBUTYL NITRITE (IBN)                                  Date: 05/20/95  
Route: RESPIRATORY EXPOSURE WHOLE BODY                                                                            Time: 11:28:48  
____________________________________________________________________________________________________________________________________
         B6C3F1 MICE MALE                          CONTROL      37.5 PPM     75 PPM       150 PPM                                   
                                                                                                                                    
____________________________________________________________________________________________________________________________________
                                                                                                                                    
ALIMENTARY SYSTEM - CONT                                                                                                            
      Centrilobular, Necrosis                                                                 2 (3%)                                
      Hepatocyte, Necrosis                                                                    1 (2%)                                
      Midzonal, Fatty Change                                        1 (2%)                                                          
      Periportal, Vacuolization Cytoplasmic                                                   1 (2%)                                
   Mesentery                                                       (1)          (5)          (2)                                    
      Artery, Inflammation, Chronic Active                                       1 (20%)                                            
      Fat, Necrosis                                                 1 (100%)     2 (40%)      2 (100%)                              
   Pancreas                                           (60)         (59)         (60)         (56)                                   
      Inflammation, Chronic                            3 (5%)                                 3 (5%)                                
      Inflammation, Chronic Active                                               1 (2%)                                             
      Proliferation Connective Tissue                                                         1 (2%)                                
      Acinus, Atrophy                                  1 (2%)       1 (2%)       1 (2%)       1 (2%)                                
      Duct, Cyst                                                                              1 (2%)                                
   Salivary Glands                                    (60)         (60)         (60)         (60)                                   
      Inflammation, Chronic                           36 (60%)     33 (55%)     29 (48%)     29 (48%)                               
   Stomach, Glandular                                 (59)         (59)         (59)         (56)                                   
      Dysplasia                                                                               1 (2%)                                
      Necrosis                                                      1 (2%)       1 (2%)       2 (4%)                                
      Ulcer                                                                      1 (2%)                                             
   Tooth                                              (3)                       (1)          (1)                                    
      Dysplasia                                        1 (33%)                                                                      
____________________________________________________________________________________________________________________________________
                                                                                                                                    
 CARDIOVASCULAR SYSTEM                                                                                                              
                                                                                                                                    
   Heart                                              (60)         (60)         (60)         (60)                                   
      Cardiomyopathy                                                                          1 (2%)                                
      Degeneration                                                                            1 (2%)                                
      Mineralization                                   1 (2%)                                                                       
      Thrombosis                                                                              1 (2%)                                
      Artery, Inflammation, Chronic Active                                       1 (2%)       1 (2%)                                
____________________________________________________________________________________________________________________________________
                                                                                                                                    
 ENDOCRINE SYSTEM                                                                                                                   
                                                                                                                                    
   Adrenal Cortex                                     (59)         (59)         (58)         (58)                                   
      Cyst                                                          3 (5%)       1 (2%)                                             
      Hyperplasia                                                                1 (2%)                                             
      Hypertrophy, Focal                               6 (10%)     16 (27%)     10 (17%)      9 (16%)                               
      Capsule, Accessory Adrenal Cortical Nodule       2 (3%)                    1 (2%)                                             
      Subcapsular, Hyperplasia                        33 (56%)     26 (44%)     18 (31%)     24 (41%)                               
   Adrenal Medulla                                    (59)         (59)         (58)         (58)                                   
      Hyperplasia, Focal                                                         2 (3%)                                             
   Islets, Pancreatic                                 (5)          (3)          (9)          (1)                                    
      Hyperplasia, Focal                               3 (60%)      3 (100%)     7 (78%)      1 (100%)                              
   Pituitary Gland                                    (56)         (56)         (54)         (54)                                   
      Pars Distalis, Cyst                              1 (2%)                                                                       
a  Number of animals examined microscopically at site and number of animals with lesion                                             
                                                             Page   10                                                              
NTP Experiment-Test: 05185-04         INCIDENCE RATES OF NONNEOPLASTIC LESIONS BY ANATOMIC SITE (a)               Report: PEIRPT03
Study Type: CHRONIC                                       ISOBUTYL NITRITE (IBN)                                  Date: 05/20/95  
Route: RESPIRATORY EXPOSURE WHOLE BODY                                                                            Time: 11:28:48  
____________________________________________________________________________________________________________________________________
         B6C3F1 MICE MALE                          CONTROL      37.5 PPM     75 PPM       150 PPM                                   
                                                                                                                                    
____________________________________________________________________________________________________________________________________
                                                                                                                                    
ENDOCRINE SYSTEM - CONT                                                                                                             
      Pars Distalis, Hyperplasia                       1 (2%)                    1 (2%)                                             
      Pars Distalis, Hyperplasia, Focal                             1 (2%)       1 (2%)                                             
   Thyroid Gland                                      (60)         (60)         (60)         (60)                                   
      Ultimobranchial Cyst                                                       1 (2%)                                             
      Follicular Cell, Hyperplasia                                               1 (2%)                                             
      Follicular Cell, Hyperplasia, Focal              8 (13%)     17 (28%)     12 (20%)     20 (33%)                               
____________________________________________________________________________________________________________________________________
                                                                                                                                    
 GENERAL BODY SYSTEM                                                                                                                
                                                                                                                                    
   None                                                                                                                             
____________________________________________________________________________________________________________________________________
                                                                                                                                    
 GENITAL SYSTEM                                                                                                                     
                                                                                                                                    
   Epididymis                                         (60)         (60)         (60)         (60)                                   
      Inflammation, Chronic Active                     1 (2%)       2 (3%)       3 (5%)       8 (13%)                               
      Spermatocele                                                  1 (2%)                                                          
   Penis                                              (1)          (1)          (1)          (5)                                    
      Congestion                                                                              1 (20%)                               
      Inflammation, Chronic Active                     1 (100%)                  1 (100%)     3 (60%)                               
   Preputial Gland                                    (19)         (22)         (18)         (14)                                   
      Abscess                                                       3 (14%)      2 (11%)      1 (7%)                                
      Dilatation                                      16 (84%)     14 (64%)     17 (94%)     11 (79%)                               
      Inflammation, Chronic Active                     6 (32%)      6 (27%)      5 (28%)      4 (29%)                               
   Prostate                                           (60)         (59)         (59)         (60)                                   
      Hyperplasia, Focal                                                         1 (2%)                                             
      Inflammation, Acute                                           1 (2%)                    2 (3%)                                
      Inflammation, Chronic Active                     1 (2%)       1 (2%)       4 (7%)       3 (5%)                                
   Seminal Vesicle                                    (60)         (60)         (60)         (60)                                   
      Dilatation                                       4 (7%)       7 (12%)     12 (20%)      3 (5%)                                
      Hyperplasia                                                                             1 (2%)                                
      Inflammation, Acute                                           1 (2%)                                                          
      Inflammation, Chronic Active                                               1 (2%)       1 (2%)                                
   Testes                                             (60)         (60)         (60)         (60)                                   
      Mineralization                                                             1 (2%)                                             
      Spermatocele                                     1 (2%)                                                                       
      Seminiferous Tubule, Degeneration                2 (3%)                                 1 (2%)                                
      Tunic, Inflammation, Chronic                                               1 (2%)                                             
      Tunic, Proliferation Connective Tissue                                     1 (2%)                                             
____________________________________________________________________________________________________________________________________
                                                                                                                                    
a  Number of animals examined microscopically at site and number of animals with lesion                                             
                                                             Page   11                                                              
NTP Experiment-Test: 05185-04         INCIDENCE RATES OF NONNEOPLASTIC LESIONS BY ANATOMIC SITE (a)               Report: PEIRPT03
Study Type: CHRONIC                                       ISOBUTYL NITRITE (IBN)                                  Date: 05/20/95  
Route: RESPIRATORY EXPOSURE WHOLE BODY                                                                            Time: 11:28:48  
____________________________________________________________________________________________________________________________________
         B6C3F1 MICE MALE                          CONTROL      37.5 PPM     75 PPM       150 PPM                                   
                                                                                                                                    
____________________________________________________________________________________________________________________________________
                                                                                                                                    
 HEMATOPOIETIC SYSTEM                                                                                                               
                                                                                                                                    
   Bone Marrow                                        (60)         (60)         (59)         (59)                                   
      Infarct                                                                                 1 (2%)                                
      Myeloid Cell, Hyperplasia                        3 (5%)       5 (8%)       7 (12%)      9 (15%)                               
   Lymph Node                                         (1)          (5)          (5)          (5)                                    
      Iliac, Infiltration Cellular, Histiocyte                                   1 (20%)                                            
      Iliac, Inflammation, Chronic Active                                                     1 (20%)                               
      Inguinal, Hyperplasia, Lymphoid                                            2 (40%)                                            
      Inguinal, Inflammation, Chronic Active                                                  1 (20%)                               
      Inguinal, Pigmentation                                                                  1 (20%)                               
      Lumbar, Hemorrhage                                                                      1 (20%)                               
      Lumbar, Hyperplasia, Histiocytic                                                        1 (20%)                               
      Lumbar, Hyperplasia, Lymphoid                                 1 (20%)                   1 (20%)                               
      Lumbar, Hyperplasia, Plasma Cell                                                        1 (20%)                               
      Renal, Hyperplasia, Plasma Cell                               1 (20%)      1 (20%)                                            
   Lymph Node, Bronchial                              (33)         (45)         (26)         (39)                                   
      Hemorrhage                                                    1 (2%)                                                          
      Hyperplasia, Lymphoid                                         1 (2%)       1 (4%)       1 (3%)                                
      Infiltration Cellular, Histiocyte                                                       1 (3%)                                
      Inflammation, Chronic Active                                               1 (4%)                                             
   Lymph Node, Mandibular                             (49)         (59)         (60)         (55)                                   
      Hemorrhage                                                                              1 (2%)                                
      Hyperplasia, Lymphoid                            1 (2%)       1 (2%)                    1 (2%)                                
      Pigmentation, Hemosiderin                                                               1 (2%)                                
   Lymph Node, Mesenteric                             (57)         (57)         (57)         (56)                                   
      Angiectasis                                                                1 (2%)                                             
      Hematopoietic Cell Proliferation                              1 (2%)       1 (2%)                                             
      Hemorrhage                                       2 (4%)       4 (7%)       5 (9%)       6 (11%)                               
      Hyperplasia, Lymphoid                            3 (5%)       1 (2%)                    1 (2%)                                
      Hyperplasia, Plasma Cell                                                   2 (4%)                                             
   Lymph Node, Mediastinal                            (48)         (47)         (48)         (46)                                   
      Hemorrhage                                       1 (2%)                    1 (2%)       1 (2%)                                
      Hyperplasia, Lymphoid                                                                   2 (4%)                                
      Hyperplasia, Plasma Cell                                                                1 (2%)                                
   Spleen                                             (60)         (60)         (59)         (58)                                   
      Fibrosis                                                                                1 (2%)                                
      Hematopoietic Cell Proliferation                59 (98%)     53 (88%)     57 (97%)     55 (95%)                               
      Hematopoietic Cell Proliferation Granulocytic                              1 (2%)       2 (3%)                                
      Hyperplasia, Lymphoid                                         2 (3%)                                                          
      Pigmentation, Hemosiderin                       34 (57%)     26 (43%)     55 (93%)     56 (97%)                               
      Lymphoid Follicle, Atrophy                                                              2 (3%)                                
   Thymus                                             (55)         (56)         (48)         (50)                                   
      Atrophy                                         13 (24%)     12 (21%)      7 (15%)      9 (18%)                               
      Cyst                                                                                    1 (2%)                                
      Ectopic Parathyroid Gland                                                               1 (2%)                                
      Hyperplasia, Lymphoid                                                      1 (2%)       1 (2%)                                
____________________________________________________________________________________________________________________________________
a  Number of animals examined microscopically at site and number of animals with lesion                                             
                                                             Page   12                                                              
NTP Experiment-Test: 05185-04         INCIDENCE RATES OF NONNEOPLASTIC LESIONS BY ANATOMIC SITE (a)               Report: PEIRPT03
Study Type: CHRONIC                                       ISOBUTYL NITRITE (IBN)                                  Date: 05/20/95  
Route: RESPIRATORY EXPOSURE WHOLE BODY                                                                            Time: 11:28:48  
____________________________________________________________________________________________________________________________________
         B6C3F1 MICE MALE                          CONTROL      37.5 PPM     75 PPM       150 PPM                                   
                                                                                                                                    
____________________________________________________________________________________________________________________________________
                                                                                                                                    
                                                                                                                                    
 INTEGUMENTARY SYSTEM                                                                                                               
                                                                                                                                    
   Skin                                               (60)         (60)         (59)         (59)                                   
      Inflammation, Chronic                            1 (2%)                                 2 (3%)                                
      Inflammation, Chronic Active                                  3 (5%)       2 (3%)       3 (5%)                                
      Ulcer                                                         2 (3%)                    2 (3%)                                
      Epithelium, Hyperplasia                                       1 (2%)       1 (2%)                                             
      Fat, Necrosis                                    1 (2%)                                                                       
      Hair Follicle, Atrophy                           1 (2%)                                                                       
      Prepuce, Inflammation, Chronic Active            1 (2%)                    1 (2%)       1 (2%)                                
      Prepuce, Ulcer                                                             1 (2%)                                             
      Subcutaneous Tissue, Edema                                                              1 (2%)                                
      Subcutaneous Tissue, Granuloma                                                          1 (2%)                                
      Subcutaneous Tissue, Hemorrhage                                                         1 (2%)                                
____________________________________________________________________________________________________________________________________
                                                                                                                                    
 MUSCULOSKELETAL SYSTEM                                                                                                             
                                                                                                                                    
   Bone                                               (60)         (60)         (60)         (60)                                   
      Developmental Malformation                                                 1 (2%)                                             
      Dysplasia                                                                  1 (2%)                                             
      Fracture                                                                                1 (2%)                                
      Hyperostosis                                                  1 (2%)                                                          
      Cartilage, Degeneration                                       1 (2%)                                                          
      Maxilla, Callus                                  1 (2%)                                                                       
      Maxilla, Fracture                                2 (3%)                                                                       
   Skeletal Muscle                                                 (1)          (1)                                                 
      Inflammation, Chronic Active                                               1 (100%)                                           
____________________________________________________________________________________________________________________________________
                                                                                                                                    
 NERVOUS SYSTEM                                                                                                                     
                                                                                                                                    
   Brain                                              (60)         (60)         (60)         (60)                                   
      Mineralization                                  41 (68%)     36 (60%)     31 (52%)     24 (40%)                               
____________________________________________________________________________________________________________________________________
                                                                                                                                    
 RESPIRATORY SYSTEM                                                                                                                 
                                                                                                                                    
   Larynx                                             (60)         (60)         (59)         (57)                                   
      Inflammation, Acute                                           1 (2%)                                                          
      Inflammation, Chronic Active                                  1 (2%)                                                          
   Lung                                               (60)         (60)         (59)         (60)                                   
      Congestion                                                                              1 (2%)                                
      Infiltration Cellular, Lymphocyte                1 (2%)       3 (5%)       2 (3%)       3 (5%)                                
      Inflammation, Chronic Active                     3 (5%)                                                                       
      Leukocytosis                                                                            1 (2%)                                
      Alveolar Epithelium, Hyperplasia, Focal          1 (2%)       4 (7%)       7 (12%)     13 (22%)                               
a  Number of animals examined microscopically at site and number of animals with lesion                                             
                                                             Page   13                                                              
NTP Experiment-Test: 05185-04         INCIDENCE RATES OF NONNEOPLASTIC LESIONS BY ANATOMIC SITE (a)               Report: PEIRPT03
Study Type: CHRONIC                                       ISOBUTYL NITRITE (IBN)                                  Date: 05/20/95  
Route: RESPIRATORY EXPOSURE WHOLE BODY                                                                            Time: 11:28:48  
____________________________________________________________________________________________________________________________________
         B6C3F1 MICE MALE                          CONTROL      37.5 PPM     75 PPM       150 PPM                                   
                                                                                                                                    
____________________________________________________________________________________________________________________________________
                                                                                                                                    
RESPIRATORY SYSTEM - CONT                                                                                                           
      Alveolus, Infiltration Cellular, Histiocyte                   1 (2%)       2 (3%)       2 (3%)                                
   Nose                                               (60)         (60)         (60)         (60)                                   
      Exudate                                                                    1 (2%)                                             
      Exudate, Serous                                                                         2 (3%)                                
      Inflammation, Chronic Active                     8 (13%)      8 (13%)      7 (12%)     10 (17%)                               
      Olfactory Epithelium, Atrophy                                              1 (2%)       1 (2%)                                
      Olfactory Epithelium, Degeneration, Hyaline                   4 (7%)       2 (3%)       2 (3%)                                
      Olfactory Epithelium, Metaplasia                 3 (5%)       1 (2%)       3 (5%)       1 (2%)                                
      Respiratory Epithelium, Degeneration, Hyaline    4 (7%)       3 (5%)       3 (5%)       3 (5%)                                
      Respiratory Epithelium, Hyperplasia             13 (22%)     20 (33%)     19 (32%)      8 (13%)                               
      Respiratory Epithelium, Metaplasia, Squamous                  3 (5%)                    3 (5%)                                
      Respiratory Epithelium, Ulcer                                 2 (3%)                    1 (2%)                                
____________________________________________________________________________________________________________________________________
                                                                                                                                    
 SPECIAL SENSES SYSTEM                                                                                                              
                                                                                                                                    
   Eye                                                                          (1)          (2)                                    
      Phthisis Bulbi                                                             1 (100%)     1 (50%)                               
      Cornea, Inflammation, Chronic Active                                                    1 (50%)                               
      Lens, Cataract                                                                          1 (50%)                               
   Harderian Gland                                    (5)          (1)          (3)          (6)                                    
      Inflammation, Chronic Active                                  1 (100%)                                                        
____________________________________________________________________________________________________________________________________
                                                                                                                                    
 URINARY SYSTEM                                                                                                                     
                                                                                                                                    
   Kidney                                             (60)         (60)         (60)         (60)                                   
      Abscess                                                                                 1 (2%)                                
      Amyloid Deposition                                            1 (2%)                                                          
      Cyst                                             2 (3%)       1 (2%)       2 (3%)       2 (3%)                                
      Hydronephrosis                                   2 (3%)       2 (3%)                    5 (8%)                                
      Infarct                                                                    2 (3%)       1 (2%)                                
      Infiltration Cellular, Lymphocyte               17 (28%)     18 (30%)     13 (22%)     23 (38%)                               
      Inflammation, Acute                                           1 (2%)                    2 (3%)                                
      Inflammation, Chronic Active                     1 (2%)       3 (5%)       5 (8%)       6 (10%)                               
      Metaplasia, Osseous                              1 (2%)                    1 (2%)                                             
      Mineralization                                                             1 (2%)                                             
      Nephropathy                                      1 (2%)       1 (2%)                                                          
      Artery, Inflammation, Chronic Active                                       1 (2%)                                             
      Renal Tubule, Dilatation                         1 (2%)       3 (5%)                    6 (10%)                               
      Renal Tubule, Hyperplasia, Focal                 1 (2%)                    2 (3%)       2 (3%)                                
      Renal Tubule, Regeneration                      12 (20%)      6 (10%)      5 (8%)       4 (7%)                                
   Urinary Bladder                                    (60)         (58)         (59)         (57)                                   
      Dilatation                                       7 (12%)      7 (12%)     14 (24%)      9 (16%)                               
      Infiltration Cellular, Lymphocyte                2 (3%)       4 (7%)       1 (2%)       5 (9%)                                
      Inflammation, Acute                                           1 (2%)                    1 (2%)                                
      Inflammation, Chronic Active                     2 (3%)       3 (5%)       5 (8%)       8 (14%)                               
a  Number of animals examined microscopically at site and number of animals with lesion                                             
                                                             Page   14                                                              
NTP Experiment-Test: 05185-04         INCIDENCE RATES OF NONNEOPLASTIC LESIONS BY ANATOMIC SITE (a)               Report: PEIRPT03
Study Type: CHRONIC                                       ISOBUTYL NITRITE (IBN)                                  Date: 05/20/95  
Route: RESPIRATORY EXPOSURE WHOLE BODY                                                                            Time: 11:28:48  
____________________________________________________________________________________________________________________________________
         B6C3F1 MICE MALE                          CONTROL      37.5 PPM     75 PPM       150 PPM                                   
                                                                                                                                    
____________________________________________________________________________________________________________________________________
                                                                                                                                    
URINARY SYSTEM - CONT                                                                                                               
      Transitional Epithelium, Hyperplasia                          1 (2%)       1 (2%)                                             
                                                                                                                                    
a  Number of animals examined microscopically at site and number of animals with lesion                                             
                                                             Page   15                                                              
                             ------------------------------------------------------------                                           
                             ----------              END OF REPORT             ----------                                           
                             ------------------------------------------------------------