Plasma amino acid concentrations were measured during fasting and after 3 days of enteral feeding in 16 trauma patients on a glutamine-supplemented diet and 14 patients on an isonitrogenous control diet. During fasting, total amino acids, including glutamine, were depressed by 50% and this was attributed to a reduction in both essential and nonessential amino acids. The essential amino acid concentrations increased in both groups after feeding. The nonessential amino acid concentrations also increased in the control group but not in the glutamine group during feeding. Repletion of the glutamine extracellular pool was not evident after an average intake of 27.1 g per day of glutamine for 3 days. Nitrogen balance was similar for the two groups during feeding. We conclude that in this study, enteral glutamine did not increase the glutamine plasma concentration. In addition, both formulas improved the hypoaminoacidemia of essential amino acids but only the control diet improved the nonessential amino acids plasma concentration.