The literature of 506 chemicals has been evaluated for evidence that these chemicals induce tumors in experimental animals and this assessment comprises the Gene-Tox Carcinogen Data Base. Three major sources of information were used to create the evaluated data base: all 185 chemicals determined by the International Agency for Research on Cancer to have Sufficient evidence of carcinogenic activity in experimental animals, 28 selected chemicals bioassayed for carcinogenic activity by the National Toxicology Program/National Cancer Institute and found to induce tumors in mice and rats, and 293 selected chemicals which has been evaluated in genetic toxicology and related bioassays as determined from previous Gene-Tox reports. The literature data on the 293 chemicals were analyzed by the Gene-Tox Carcinogenesis Panel in an organized, rational, and consistent manner. Criteria were established to assess individual studies employing single chemical and four categories of response were developed: Positive, Negative, Inconclusive (Equivocal), and Inconclusive. After evaluating each of the individual studies on the 293 chemicals, the Panel placed each of the 506 chemicals in an overall classification category based on the strength of the evidence indicating the presence or absence of carcinogenic effects. An eight-category decision scheme was established using a modified version of the International Agency for Research on Cancer approach.