Pretreatment with ethyl alcohol, 0.5 hr before exposure to 0.1 mg/m3 of mercury vapor, resulted in markedly lower retention of mercury as compared with the nonalcohol-treated controls. The decrease in whole-body mercury retention was related to the dose of alcohol (0.25-6.0 g/kg). Near maximum reduction in mercury concentration in blood, brain, heart and lung was obtained at a 1 g/kg alcohol dose. However, mercury concentration in kidney was not significantly reduced even at a 2 g/kg alcohol dose and was significantly elevated in liver up to a 3 g/kg alcohol dose; higher doses of alcohol produced a linear decrease in both renal and hepatic mercury concentrations. A part of the decrease in whole-body mercury level was ascribed to the sedative effect of alcohol as indicated by results from rats treated with pentobarbital. Studies in rats treated with 3-aminotriazole indicated that alcohol probably also acted by inhibition of catalase-mediated oxidation of mercury vapor. Administration of pyrazole resulted in augmentation of the effect of alcohol, suggesting that alcohol itself, rather than its metabolites, was responsible for the inhibition of mercury vapor oxidation.