The metabolism of benzo(a)pyrene (BaP) by hepatic or cheek pouch epithelium microsomes obtained from Syrian golden hamsters which had been consuming an ethanol-containing liquid diet for 4 wk and from pair-fed controls was measured. Glutathione S-transferase activity with 1-chloro-2,4-dinitrobenzene or (+/-)-r-7,t-8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene as substrates was measured in cytosol obtained from the liver or cheek pouch epithelium of the same animals. Cytosolic hepatic glutathione levels were measured in both ethanol-consuming and control animals. The metabolism of BaP to 4,5-dihydro-4,5-dihydroxybenzo(a)pyrene (BaP-4,5-diol), 7,8-dihydro-7,8-dihydroxybenzo(a)pyrene (BaP-7,8-diol), 9-hydroxybenzo(a)pyrene (9-OH-BaP), and 3-hydroxybenzo(a)pyrene (3-OH-BaP) by hepatic microsomes from ethanol-consuming hamsters was significantly reduced (40-52%) (P less than 0.05) compared to control microsomes. However, a 2-fold increase (P less than 0.05) in the metabolism of BaP to BaP-7,8-diol and 9,10-dihydro-9,10-dihydroxybenzo(a)pyrene was measured with microsomes from the cheek pouch epithelium of ethanol-consuming animals. There was no significant change in the production of BaP-4,5-diol, 9-OH-BaP, or 3-OH-BaP by cheek pouch epithelium microsomes of ethanol-consuming hamsters compared to controls. No difference in glutathione S-transferase activity of hepatic or cheek pouch epithelium cytosol between control and ethanol-consuming hamsters towards 1-chloro-2,4-dinitrobenzene or (+/-)-r-7,t-8-dihydroxy-t-9,10- epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene was observed. Hepatic glutathione content was significantly (P less than 0.05) decreased after 2 wk (23%) and 4 wk (33%) of ethanol consumption. The results suggest a mechanism by which ethanol might enhance BaP tumorigenesis in the hamster cheek pouch.