Ally alcohol is metabolized in the liver through two steps, first to reactive acrolein by alcohol dehydrogenase(ADH), subsequently to acrylic acid by aldehyde dehydrogenase(ALDH). Since ethanol could compete the same enzymes to be metabolized in the liver, we have studied the interaction between allyl alcohol and ethanol on liver toxicity. Simultaneous treatment of 2 g/kg ethanol by ip administration with 40 mg/kg allyl alcohol to rats increased the lethality significantly, accompanied by potentiation of the loss of hepatic glutathione. Collectively, these findings suggested that ethanol potentiated the hepatotoxicity and lethality induced by allyl alcohol probably through competing two metabolizing enzymes, ADH and ALDH.