We observed the effect of the administration of vitamin A,C and E with β-naphthoflavone and piperonyl butoxide on cytochrome P-450 level and lipid peroxidation in rats liver. The level of hepatic cytochrome P-450 decreased after vitamin A,C and E was administration. In contrast, β-naphthoflavone, when administered with vitamin A,C and E, the increase of cytochrome P-450 was prevented. Lipid peroxidation was decreased after vitamin A, C, and E was administered. Moreover when β-naphthoflavone was administered together with vitamin A, C and E lipid peroxidation was not increased. When piperonyl butoxide was administered together with vitamin A,C and E, both cytochrome P-450 and lipid peroxidation were decreased. These results indicate that vitamin antioxidants can prevent lipid peroxidation by a cytochrome P-450 dependent terminal oxidase system in rat liver microsomes.