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Toxicology in the 21st Century (Tox21)

Robotic arm used for Tox21 testing

The Toxicology in the 21st Century (Tox21) program is a federal collaboration among the National Institutes of Health, including the National Toxicology Program (NTP) at the National Institute of Environmental Health Sciences and the National Center for Advancing Translational Sciences, the Environmental Protection Agency, and the Food and Drug Administration.

Tox21 researchers utilize a screening method called high throughput screening (HTS) that uses automated methods to quickly and efficiently test chemicals for activity across a battery of assays that target cellular processes. These assays are useful for rapidly evaluating large numbers of chemicals to provide insight on potential human health effects. The HTS initiative in NTP was developed in response to the 2004 NTP vision and roadmap, “A National Toxicology Program for the 21st Century: A Roadmap for the Future.”

Through HTS, the collaboration is testing a collection of more than 10,000 environmental chemicals, drugs, and formulations to broadly characterize and define their chemical reactivity in biochemical- and cell-based assays.

Building on the strengths of each partner, Tox21 facilitates the advancement of toxicology to a more predictive science, based on the most relevant and meaningful tools of modern molecular biology and chemistry. The convergence of science, technology, regulatory need, and public opinion has created the opportunity to transform toxicology and risk assessment into more accurate, rapid, and cost-effective sciences.

Additionally, Tox21 supports the goals of reduction, refinement, and replacement of animals in toxicity testing (NTP Interagency Center for the Evaluation of Alternative Toxicological Methods Tox21 activities).

Goals of the Tox21 Program

The goal of Tox21 is to research, develop, validate, and translate innovative test methods that will better predict how chemicals may affect humans and the environment. Tox21 researchers hope to use the results from these methods to:

  • Prioritize substances for further in-depth toxicological evaluation
  • Identify mechanisms of action for further investigation (e.g., disease-associated pathways)
  • Develop models that better predict how chemicals will affect biological responses (predictive toxicology)


For further information on NTP's Tox21 program, contact: