AbstractMale Sprague‐Dawley rats were maintained on a vitamin A‐deficient diet for a period of five weeks. At the end of that time, hepatic cytochrome P450levels in vitamin A‐deficient rats were 65% that of rats fed a complete diet. However, the hepatic rate of benzo[a]pyrene metabolism was significantly greater (2 times) in vitamin A‐deficient rats compared with those fed a complete diet. The pattern of metabolites separable by thin‐layer chromatography was similar in both groups of rats. Benzo[a]pyrene induced its own metabolism by a slightly greater amount in the vitamin‐sufficient rats, but it was not to the level of the deficient group, although the levels of cytochrome P450were still below those of the deficient rats. In discussing lung microsomes, benzo[a]pyrene pre‐treatment of deficient rats resulted in slightly elevated levels of cytochrome P450and a slightly greater rate of metabolism of benzo[a]pyrene compared with rats fed the complete diet.