The branched-chain amino acids (BCAA)-leucine, isoleucine, and valine are three of nine amino acids, that cannot be synthesized by animals and are therefore essential nutrients that must be obtained from foods. They are required specifically for the synthesis of proteins, not as precursors of unique biologically active molecules. The BCAA comprise about 35% of the indis pensable amino acids in muscle proteins and about 40% of the amino acids required preformed by mammals. As the BCAA make up almost 50% of the indispensable amino acids in the food supply, deficiencies of them do not occur naturally (92). Nutritional investigations of the BCAA have therefore focused primarily on the effects of excessive intakes of the individual BCAA and on the metabolic relationships among them, rather than on problems relating to inadequate intakes.