The effect of acute ethanol (3 g/kg and 5 g/kg) or corticosterone (12.5 mg/kg) on benzo(a)pyrene metabolism was measured in microsomes from 3-methylcholanthrene pretreated rats. BAP disappearance was inhibited 34% at 5 g/kg but unaltered at 3 g/kg ethanol. Corticosterone administration inhibited BAP metabolism 53%. In adrenalectomized (ADX) rats, alcohol or CS did not decrease BAP metabolism (compared to untreated ADX rats). However, corticosterone in vitro inhibited BAP metabolism in a dose-related fashion in washed microsomes from untreated rats. These results demonstrate that acute ethanol and corticosterone administration alter benzo(a)pyrene metabolism. Furthermore, the inhibition requires an intact adrenal.