Objectives: To coordinate and manage the Carcinogen Bioassay Program which identifies and evaluates carcinogenic hazards of chemical and physical agents in the environment. Approximately 540 chemicals were on test this year at contract laboratories using standardized long-term animal bioassay tests to assess for carcinogenicity. Considerable planning is required to procure and coordinate the animal, chemical, information and laboratory resources required for an efficient and quality operation. A Chemical Selection Working Group selects chemicals on the basis of human exposure and production data, and chemical structure. Nominations of chemicals for testing come from various sources including other Federal agencies. The main animals used in the Bioassay Program are the Fisher/344 and Osborne-Mendel rats and B6C3F1 hybrid mouse (C57B1/6 x C3H). Most of the animal needs are supplied by the Frederick Cancer Research Center. Bioassay data is recorded and analyzed by use of a computerized data system known as the Carcinogenesis Bioassay Data System (CBDS). Final results are published in scientific journals and technical reports. A prime contract is now used to assist in the administrative and scientific management of the testing program.