This study considers the effects of glucose, during amino acid infusion, on protein-sparing and amino acid utilization after proctocolectomy or abdominoperineal resection of the rectum. Body composition and plasma amino acids were compared in each of three groups of patients before and 15 days after surgery who were receiving, in addition to restricted oral diets: 1) no hyperalimentation 2) parenteral amino acids or 3) hypertonic glucose plus amino acids. Parenteral solutions were given by central venous catheter. Infusion of amino acids alone spared body protein but branch chain amino acids (i.e. valine, isoleucine and leucine) and also phenylalanine, methionine and proline were increased well above the normal values. There were no increases in liver proteins other than for the "acute phase" type. In contrast, full hyperalimentation spared more body protein and fat, restored plasma amino acids to normal while plasma cortisol and acute pohase proteins were lower. Plasma transferrin, prealbumin and retinol binding protein were increased, as previously shown, while clinical outcome was more favorable. It is concluded that glucose is essential to ensure optimum utilization of amino acids for both muscle and liver protein synthesis and, therefore, intravenous hyperalimentation is preferable to amino acids alone after major colorectal surgery.