The hepatocyte primary culture/DNA repair test was evaluated for its reliability using a series of coded samples. Among the 30 chemicals tested, 15 were general reference compounds and 15 were chemicals that had been tested for carcinogenicity in the U.S. National Cancer Institute Bioassay Program. The latter group were from the same lot that had been used for the in vivo testing and had also been tested for mutagenicity in the Ames test. From the group of 15 reference compounds, 5 were positive for DNA repair and all 5 were carcinogens. Of the 10 samples scored as negative, 4 were noncarcinogens and 6 were carcinogens. Among the 6 carcinogens were 3 compounds whose carcinogenicity probably does not involve the production of DNA damage. From the 15 coded chemicals that were tested for carcinogenicity by the NCI in long-term animal studies, 7 were scored as positive. 5 of these were judged carcinogenic in the in vivo bioassays and the other 2, which were also mutagenic in Salmonella, showed some indication of carcinogenicity. Of the 8 compounds that were scored as negative, 5 were noncarcinogenic. Among the 3 carcinogens that were not detected, there was at least one whose carcinogenicity probably does not involve DNA damage. Thus, the results of this study indicate that positive results in the hepatocyte primary culture/DNA repair test are highly specific for carcinogens and that the test is also highly sensitive in the detection of DNA-damaging genotoxic carcinogens.