Glutathione is quantitatively the most important endogenous scavenger system. Glutathione depletion in skeletal muscle is pronounced following major trauma and sepsis in intensive care unit patients. Also, following elective surgery, glutathione depletion occurs in parallel with a progressive decline in muscle glutamine concentration. The present study was designed to test the hypothesis that glutamine supplementation may counteract glutathione depletion in a human trauma model. A homogeneous group of patients ( n = 17) undergoing a standardized surgical procedure were prospectively randomly allocated to receive glutamine (0.56g·day -1 ·kg -1 ) or placebo as part of isonitrogenous and isocaloric nutrition. Percutaneous muscle biopsies and blood samples were taken pre-operatively and at 24 and 72h after surgery. The concentrations of muscle glutathione and related amino acids were determined in muscle tissue and plasma. In the control (unsupplemented) subjects, total muscle glutathione had decreased by 47±8% and 37±11% and reduced glutathione had decreased by 53±10% and 45±16% respectively at 24 and 72h after surgery ( P <0.05). In contrast, in the glutamine-supplemented group, no significant post-operative decreases in total or reduced glutathione were seen following surgery. Muscle free glutamine had decreased at 72h after surgery in both groups, by 41.4±14.8% ( P <0.05) in the glutamine-supplemented group and by 46.0±14.3% ( P <0.05) in the control group. In conclusion, the present study demonstrates that intravenous glutamine supplementation attenuates glutathione depletion in skeletal muscle in humans following standardized surgical trauma.