The metabolic effects of TPN containing high amounts of amino acids (18 gm N) was evaluated with respect to sulfur amino acid metabolism and protein breakdown in nine severely burned patients. The results were compared to corresponding data from burned patients receiving more moderate amounts of amino acids (9.2 gm N) or isocaloric amounts of carbohydrate and fat.Significantly increased urinary excretion and intracellular muscle tissue concentrations of methionine were found in patients receiving the concentrated amino acid solution, probably reflecting a combined effect of the injury and an increased load of the compound. These patients also showed a reduced oxidation of sulfur amino acids to inorganic sulfate, which may reflect an increased protein synthesis during treatment. A significantly decreased urinary excretion of 3-methyl-histidine and mercaptolactate was found in patients receiving the concentrated amino acid solution, probably reflecting a decreased breakdown of body protein. The findings favor the hypothesis of an anabolic effect of the new amino acid solution in burned patients during the early catabolic phase, but also emphasize the importance of monitoring the amounts of amino acids, e.g., methionine, given.