The effects of Naloxone, narcotic antagonist, pretreated with normal saline, salicylate and hydrocortisone produced by with hypovolemic shock on the rates of cytochrome components, mixed function oxidation enzyme reactions and lipid peroxidation have been determined using hepatic microsomal fractions of rats. The treatments with either of the naloxone have increased the contents of cytochrome P-450 and b_5 and NADPH- or NADH-cytochrome C reductase. But pretreated with salicylate and hydrocortisone were not change as compared to the control. The rates of O-demethylation for p-nitroanisole were decreased. Naloxone decreased the formation of lipid peroxide by pretreated salicylate and hydrocortisone. These results indicate that naloxone showed effect not only increase of blood pressure and respiration, but also cytochrome components activity, mixed function oxidation enzyme reactions and lipid peroxidation in the hepatic microsomal fractions of rats.