By intraperitoneal administration of thioacetamide to rats, acute liver injury was produced. In these rats, the level of serum GOT and GPT activities showed a remarkable increase and the principal histopathologic change was centrilobular hepatic necrosis. In this study, combined administration of silymarin with promethazine hydrochloride to the rats with acute liver injury which was produced by thioacetamide inhibited the increase of serum transaminase activities and protected the histopathologic change, showing comparatively more improved results than simple administration of silymarin alone. On the basis of these results, it is suggested that promethazine hydrochloride potentiates the effectiveness of silymarin in acute thioacetamide hepatotoxicity of rats.