The principal role of cytochrome P-450 in many other mixed function oxidase reactions including hydroxylations or oxidative dealkylations of various drugs, fatty acids, steroids, pesticides, and carcinogens. In order to elucidate the effect of various vitamin antioxidants on hepatic microsomal cytochrome P-450 and AAF hydroxylation, vitamin antioxidants, including vitamiin A acetate, L-ascorbic acid and DL-α-tocopherol were administered to rats. The results of this study show that the inhibition of cytochrome P-450 level and AAF hydroxylation by vitamin antioxidants may be related to their ability to prevent the in vivo activation of AAF to carcinogenic N-hydroxylation. Vitamin antioxidants, because of their effectiveness in inhibiting chemical carcinogenesis, may become useful chemoprophylatic agents against environmental carcinogens.