Current solution formulations for total parenteral nutrition (TPN) do not contain glutamine (GLN). The purpose of this study was to examine whether GLN supplementation of TPN would improve survival in experimental Escherichia coli peritonitis in Fischer 344 rats (190–210 g). Initial experiments were performed to determine the degree of stress and to evaluate survival after intraperitoneal Ecoliinjection. The E coli colony used was isolated from a culture of human blood. Graded doses were injected intraperitoneally in Fischer 344 rats (190–210 g). The response of white blood cell count, plasma insulin, glucagon, and corticosterone levels, and urinary excretion of vanillylmandelic acid reflected a significant stress response for at least 3 days. Survival was dose‐dependent, with 60% mortality at 3 days after injection of 5 × 105colony forming units of Ecoli/200 g body weight. To determine whether GLN supplementation of TPN would alter survival in this E coli peritonitis model, Fischer 344 rats were randomized to receive TPN containing 4.25% standard amino acids (group STD, n = 38) or the same solution with 1.5% of the amino acid content replaced with L‐GLN (group GLN, n = 38). After 7 days of TPN, 5 × 105 colony forming units of Ecoli/200 g body weight were injected intraperitoneally under direct vision through a small laparotomy. Survival was monitored for 3 days. Surviving rats were killed to determine various nutritional parameters including plasma albumin and GLN concentration, the weight and nitrogen content of the gastrocnemius muscle, and biochemical and histological composition of the small intestine. Group GLN showed significantly improved survival (92.1%) compared with group STD (44.7%). There were no differences in the nutritional status. Mucosal weight, mucosal nitrogen content, villous height, and mucosal thickness, however, were significantly greater in group GLN than in group STD. These data demonstrate that GLN supplementation of TPN significantly improves tolerance to E coli‐induced peritonitis. Several possible mechanisms of action are discussed. (Journal of ParenteralandEnteral Nutrition 17:41–46, 1993)