A Task la study in CD-1 mice on ddC at dose levels of 200, 400, and 1000 mg/kg/day was conducted. The only toxicity observed in the males was a mild macrocytic hyperchromic anemia at the 1000 mg/kg/day dose. Similarly, maternal toxicity in the form of macrocytic hyperchromic anemia was observed at 1000 mg/kg/day in the female group. Reproductive and developmental toxicity was produced by the 400 and 1000 mg/kg/day dosages. Observations at the 1000 mg/kg/day dose included increased resorption rates, embryolethality, decreased fetal and pups weights, and gross external malformations. Observations at 400 mg/kg/day were limited to decreased fetal and pup weights. In males, the no observable adverse effect level for toxicity was 400 mg/kg/day. The 400 mg/kg/day dosage of ddC was the approximate NOAEL for maternal toxicity, and 200 mg/kg/day is the NOAEL for developmental toxicity.