To investigate an effect of ethanol pretreatment on the bromobenzene metabolism, the brornobenzene (400 mg/kg body wt. i. p.) was given 3 times at intervals of one day to the male rats orally pretreated with 5% ethanol throughout 2 months. In the ethanol pretreated rats, liver injuries were not demonstrated on the basis of the liver weight per body weight, serum levels of alanine aminotransferase (ALT) activity and histopathologic findings. By the bromobenzene treatment, ethanol pretreated rats showed the more decreased levels of serum ALT and liver weight/body weight(%), and decreased degree of liver damage on histopathological observation than the control group. The ethanol pretreated rats showed the more increased activities of hepatic aniline hydroxylase, glutathione Stransf erase (GST) and the more decreased contents of glutathione than the control. Concomitantly the ethanol pretreated rats showed the more decreased contents of hepatic glutathione and increased activities of GST by the bromobenzene treatment. Above results indicate that ethanol pretreatment enhance the metabolizing ability of bromobenzene in rats.