Isolated rat hepatocytes (4 X 10(6) cells/ml metabolized the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]-pyridine (PhIP) (100 microM) to at least eight different metabolites in a 4 h duration. The major metabolite formed was 4-(2-amino-1-methylimidazo[4,5-b]pyrid-6-yl)phenyl sulfate (4'-PhIP sulfate). Its rate of formation was increased in hepatocytes from PCB pretreated animals in comparison to hepatocytes from untreated animals. One of the other metabolites was the unconjugated derivative of the sulfate (4'-OH-PhIP). This metabolite was also found after in-vitro incubations of rat liver microsomes from PCB or beta-naphthoflavone pretreated animals. The evidence for the proposed structure of the major metabolite is based on [1H]NMR and UV spectroscopy, incorporation of radiolabelled sulfate and arylsulfatase-lability. The formation of 4'-PhIP sulfate was inhibited by the P-450 inhibitors alpha-naphthoflavone and metyrapone and when incubated in sulfate-free medium added the sulfotransferase inhibitor pentachlorophenol. 4'-PhIP sulfate was also the major metabolite of PhIP in the urine of exposed rat.