Stress hormones were infused for 6 h in healthy volunteers (n = 32). Free amino acid concentrations were determined in plasma and in skeletal muscle biopsy specimens. A triple hormone combination of adrenaline, cortisol, and glucagon raised the level of alanine in muscle, while glutamine, glutamate, the branched chain amino acids, the aromatic amino acids, and the basic amino acids decreased. Adrenaline alone partly reproduced this pattern, while a 6-h infusion of cortisol left the muscle free amino acids unaffected. In plasma all individual amino acids except alanine and glutamate decreased in the subjects receiving adrenaline or a triple-hormone combination. Altered plasma amino acid concentrations did not necessarily reflect changes in the tissue amino acid content. It is concluded that an infusion of a triple combination of stress hormones into healthy volunteers produces changes in muscle amino acid metabolism similar to those seen immediately after surgical trauma.