The kinetics of whole body protein metabolism in eight patients with benign disease were evaluated during perioperative isocaloric and isonitrogenous intravenous feedings. A prime infusion of 15N-glycine with determination of urinary end product enrichment and stochastic analysis was used to determine protein kinetics. Surgically induced increases in body protein turnover, synthesis and breakdown were evident on the fifth postoperative day. Abdominal operation was associated with a rise in urinary 3-methylhistidine (3MH) excretion. The postoperative alteration in the relationship between 3MH excretion and body protein breakdown suggests that even mild to moderate surgical injury induces tissue specific changes in protein metabolism. Resting energy expenditure remained unchanged from that of the preoperative levels on the fifth postoperative day. Despite significant changes in body and tissue specific protein kinetics, there is no change in the apparent efficiency of oxygen use for protein homeostasis postoperatively. The failure to observe a relationship between energy expenditure and protein metabolism suggests that only a small proportion of body oxygen uptake is directed toward protein homeostasis after elective surgical procedures. A comparison of perioperative complete intravenous feeding to hypocaloric regimens will be necessary to evaluate more fully the impact of protein and energy balance upon cellular and body protein homeostasis after injury.