It has been shown earlier that an acute dose of ethanol causes an immediate decrease in the concentration of most plasma amino acids, and that this decrease involves both beta-adrenergic and adrenocortical mechanisms. In this work is shown that the oxidation of ethanol also plays an important role in the amino acid decreasing effect. Male rats were pretreated with 4-methylpyrazole, an inhibitor of liver alcohol dehydrogenase, in doses causing an 85% inhibition of the ethanol elimination. In this group the ethanol-induced decrease in amino acids was much less pronounced than in a control group pretreated with saline.