The Gene-Tox Carcinogen Data Base is an evaluated source of cancer data on 506 chemicals, selected, in part, for their previous assessment in genetic toxicology bioassays. The data base has been analyzed for the distribution of these chemicals into chemical classes, and for the distribution of the cancer studies by route of administration, animal species, gender, major tumor sites, and tumor types. Chemicals in the database have been assessed for species specific carcinogenic effects, and these results indicate, that for mice and rats, there is a high correspondence (85%). When chemicals in the Gene-Tox Carcinogen Data Base were examined for their previous evaluation in 73 genetic toxicology bioassays, only 26 of these bioassays had 30 or more chemicals. In these 26 bioassays, the prevalence of positive chemicals was generally greater than 80-90%. This suggests that a thorough evaluation of genetic toxicology bioassays for their ability to predict carcinogenic effects in animals is premature at this time.