Intact prostate epithelial cells prepared from benign prostatic hypertrophy tissues from two patients were incubated for 2 h with N-hydroxy derivatives of 2-amino-1-methyl-6-phenylimidazo[4, 5-b]pyridine (N-OH-PhIP) or 2-amino-3,8-dimethylimidazo[4, 5-f]quinoxaline (N-OH-MeIQx). (32)P-post-labeling analysis detected PhIP and MeIQx adducts in the DNA of these cells but not in the untreated control. Adduct levels were approximately 100 times greater in N-OH-PhIP- than in N-OH-MeIQx-treated cells. Repair synthesis of DNA was observed in cells, prepared from two additional patients, treated for 24 h with these carcinogens and was greater for N-OH-PhIP than for N-OH-MeIQx. PhIP, MeIQx and their nitro derivatives did not produce repair synthesis of DNA in this system. The difference in the activity of N-OH-PhIP and N-OH-MeIQx may be due to their stability, since N-OH-MeIQx decomposed rapidly in neutral solution. Transcripts of NAT1 and NAT2 were detected by an in situ hybridization method in prostate epithelial cells, but were absent from stromal tissues. These results suggest that PhIP may be a potential carcinogen for human prostate, since cooked meats, which contain this heterocyclic amine, have been associated with human prostate cancer.