Cells from the human lymphoblastoid cell line, AHH-1, were exposed to two direct-acting mutagens, ethyl methanesulfonate (EMS) and ethyl nitrosourea (ENU), and to three carcinogens that require metabolic activation to an electrophile, benzo[a]pyrene (B(a)P), 6-aminochrysene (6-AC), and 6-nitrochrysene (6-NC); mutation induction at the HPRT locus was quantified by resistance to 6-thioguanine (6-TGr). Exposure of AHH-1 cells to either EMS or ENU resulted in a concentration-dependent increase in mutant frequency at the HPRT locus. When AHH-1 cells were exposed to B(a)P, the increase in mutant frequency at the HPRT locus was marginally significant linearly and significant quadratically. The 32P-postlabeling assay revealed the formation of DNA adducts derived from (+/-)anti-benzo[a]pyrene-trans-7,8-dihydrodiol-9,10-epoxide which may account for the increase in 6-TGr clones. Although DNA adducts could be detected by the 32P-postlabeling assay in both 6-NC- and 6-AC-treated AHH-1 cells, exposure to 6-AC or 6-NC did not result in a concentration-dependent increase in mutant frequency at the HPRT locus. Our results are consistent with the results of previous studies which indicate that EMS and ENU are effective inducers of 6-TGr clones as is B9(a)P when activated to an electrophile. In 6-NC- and 6-AC-exposed cells, low levels of N-hydroxy-6-aminochrysene-derived adducts were detected in only 6-NC-exposed cells. No 6-aminochrysene-1,2-dihydrodiol-derived adducts were detected following 6-NC or 6-AC exposure. Minimal metabolic activation of 6-NC or 6-AC by AHH-1 cells may account for the lack of a positive mutagenic response for either 6-AC or 6-NC.