The effects of cholesterol on 3,2'-dimethyl-4-aminobiphenyl (DMAB)-induced rat prostate carcinogenesis were investigated in male F344 rats. Animals were given 10 subcutaneous (s.c.) injections of 50 mg/kg body weight of DMAB at 2-week intervals, each time 2 days after transfer from 1 week on 0.75 ppm of an ethinyl estradiol (EE)-supplemented diet to a basal diet. From week 20, the animals received treatment with cholesterol (2 or 1%, in the diet), saponin (1 or 0.2 mg/rat/week, s.c.), or clofibrate (0.3%, in the diet) for 40 weeks. Although serum cholesterol levels were significantly increased by administration of cholesterol itself, and were decreased by clofibrate, the incidences of atypical hyperplasias and carcinomas of the ventral prostate were very similar with all treatments. Thus, under the present conditions, high or low cholesteremia did not affect rat prostate lesion development.