Intraperitoneal injection of rats with 2 mg/kg ring labelled 14C AFB1 (spec. act. 110 mCi/mM/nmole) showed a higher level of radioactivity in the urine of test animals on diets containing 600 mg/kg vit. E 24 h after pretreatment. Analysis of the urine by chloroform extraction, thin layer chromatography and liquid scintillation counting of the various fractions showed less aflatoxin M1 (AFM1) and less unmetabolized AFB1 in test samples than in controls. Incubation of ring labelled 14C AFB1 with hepatic 10,000 g supernatant fractions, however, showed increased metabolism of AFB1 by fractions from test animals as compared with the controls. Rate of disappearance of 14C AFB1 and the consequent formation of AFM1 was greater in the test fractions than in the controls. At 30 days all test animals showed higher levels of serum vitamin E than the controls. Hepatic aniline hydroxylase and ethyl morphine N-demethylase activities of the liver fractions and blood glutathione reductase activity were greater in the tests. P-nitroanisole-O-demethylase activity was reduced while hepatic and serum reduced glutathione levels remained basically unaltered.