A study of 50 patients was undertaken to determine the effects of an isotonic 5% crystalline amino acid solution on nitrogen balance. Patients were divided randomly into two groups: 24 receiving amino acids and 25 receiving dextrose in water. (One patient in the treatment group dropped out after one day of intravenous therapy.) Administration of amino acids postoperatively maintained nitrogen balance, as compared with controls. No untoward metabolic changes or other complications occurred. Amino acid peripherally administered is an alternate source of calories and nitrogen. It is of value in treating short-term undernutrition.