The multiple intestinal neoplasia (Min) mice have a mutation in the murine adenomatous polyposis coli (Apc) gene rendering them highly susceptible to spontaneous intestinal adenoma formation, similar to the familial adenomatous polyposis (FAP) syndrome in humans. We studied whether the most abundant mutagenic heterocyclic amine isolated from cooked food, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), could influence early intestinal neoplasia in C57BL/6J-Min/+ and C57BL/6J- +/+ (wild-type) mice of both sexes. PhIP was given in 4 weekly i.p. injections of 50 mg/kg. Ten weeks after the start of the experiment, PhIP had significantly increased the numbers of small tumors and cystic crypts in the proximal section of the small intestine in male Min/+ mice, and the numbers of aberrant crypt foci (ACF) in the large intestines of both males and females. The effects of PhIP were more pronounced in male than in female Min/+ mice. In +/+ mice, no tumors or cystic crypts in the small intestine, and no tumors and only a very few ACF in the large intestine, were induced by PhIP. These results show that a substance frequently present in the human diet is able to enhance the neoplastic process induced by a genetic lesion, which is also commonly found both in inherited and sporadic colon carcinomas in humans.