Plasma amino acid abnormalities in rats treated with large doses of sake and whisky for 3 days were investigated under adequate nutritional conditions. A significant decrease in plasma branched-chain amino acid (BCAA) levels was observed in sake- but not whisky-treated rats. However, known factors affecting BCAA levels, such as serum insulin and plasma glucagon levels ahd BCAA-metabolizing enzyme (BCAA transaminase and branched chain alpha-ketoacid dehydrogenase) activities in the liver and skeletal muscle, were not significantly altered in the sake group. Furthermore, ethanol-metabolizing enzyme (alcohol and aldehyde dehydrogenases and the microsomal ethanol-oxidizing system) activities in the liver were not altered in the sake group. Other mechanisms need to be considered for explaining the diminished levels of plasma BCAA in sake-treated rats.