The effects of a methanol extract of Rosa rugosa root and its triterpenoid glycoside, rosamultin, on hepatic lipid peroxidation and drug-metabolizing enzymes were investigated in rats treated with bromobenzene. The methanol extract of R. rugosa root reduced the activities of aminopyrine N-demethylase and aniline hydroxylase, which had been increased by bromobenzene, but rosamultin did not affect the activities of the two enzymes. Both the methanol extract and rosamultin restored the activity of epoxide hydrolase, which had also been decreased by bromobenzene. Hepatic glutathione concentrations were lowered and hepatic lipid peroxides were increased in rats intoxicated with bromobenzene. The hepatic lipid peroxidation induced by bromobenzene was prevented with the methanol extract and rosamultin. However, the decrease in glutathione was not altered by the methanol extract of R. rugosa. These results suggest that the extract of R. rugosa and its compound, rosamultin, may protect against bromobenzene-induced hepatotoxicity through, at least in part, enhanced activity of epoxide hydrolase. Antioxidant properties may contribute to the protection of R. rugosa against bromobenzene-induced hepatotoxicity.