Exposure to chemical carcinogens can often be identified by detection of DNA adduct lesions. Primary cultures of isolated rat and human hepatocytes were exposed to 2-acetyl-aminofluorene (AAF), 4-aminobiphenyl (ABP), or benzo(a)pyrene (BP). The isolated DNA (32)P-postlabeling assay. A greater total of carcinogen-DNA adducts, 2-12-fold, were observed in human hepatocytes than rate hepatocytes at the same concentrations. The predominant DNA adducts for each carcinogen were the same between rat and human cells. The N-(deoxyguanosin-8-yl)-2-aminofluorene (dG-C8-AF) was the major AAF-DNA adduct. The N-(deoxyguanosin-8-yl)-4-aminobiphenyl (dG-C8-ABP) was the major ABP-DNA adduct. In the rat N2-(10 beta, 8 alpha, 9 alpha-trihydroxy-7,8,9,10-tetrahydrobenzo(a)pyrene)yl)deoxyguanosine (dG-N2-BP) and two unidentified adducts were nearly equivalent in amount, while the major BP-DNA adducts in the humans was the dG-N2-BP. The rat hepatocyte in vitro results are comparable to the predominant adducts found with rats exposed in vivo. The two different cultures of human hepatocytes demonstrated qualitative and quantitative differences in specific DNA adducts from rat hepatocytes.