Fumonisins are metabolites of Fusarium moniliforme and other Fusarium spp. Fumonisin B1 (FB1) was hepatocarcinogenic (50 ppm, > or = 90% purity) when fed to male rats; however, neither the effects of FB1 on females nor the relationship between dietary FB1 levels and toxicity in rats has been reported. Male and female rats (three per sex per group) were fed diets fortified with 0, 15, 50 or 150 ppm FB1 (> or = 99% purity) for 4 weeks. There were no differences in general appearance or behavior among groups and significant differences in weight gain or food consumption were not found. Histopathological examinations and serum chemical profiles, including significant increases in triglycerides, cholesterol, and alkaline phosphatase, confirmed that 150 ppm FB1 was hepatotoxic to both sexes. Cortical nephrosis was found in males fed > or = 15 ppm and females fed > or = 50 ppm FB1. Both hepatic and renal lesions were consistent with those found in rats consuming F. moniliforme-infected corn. Thus, highly purified FB1 is unequivocally capable of inducing the subchronic liver and kidney lesions attributed to F. moniliforme.