The early-weaned pig develops intestinal atrophy and provides a readily accessible animal model for determining the role of dietary supplementation of glutamine (Gln, a major fuel for enterocytes) in preventing intestinal damage. Three experiments were conducted to determine the stability of dietary Gln in the acidic part of the gastrointestinal tract using pigs surgically fitted with a T-cannula in mid-duodenum (Exp. 1), and the effects of dietary Gln supplementation on the villus height and lamina propria depth of duodenum and jejunum (Exp. 2) as well as growth performance (Exp. 3) of pigs weaned at 21 d of age. Postweaning pigs were fed for 14 d corn- and soybean meal-based diets supplemented with 0.0, 0.2, 0.6 or 1.0% free L-Gln. Dietary Gln was not subject to measurable acid hydrolysis in the stomach and upper part of duodenum and was substantially available for the small intestine for metabolic utilization. Glutamine supplementation (1.0%) prevented jejunal atrophy (as indicated by villus height) during the first week postweaning and increased the gain:feed ratio (an indicator of growth performance) by 25% during the second week postweaning. Glutamine supplementation (1.0%) increased plasma concentrations of aspartate, glutamate and alanine and reduced the extent to which plasma taurine concentration fell in postweaning pigs. These results provide an experimental basis for enteral use of Gln in swine production and clinical nutrition to prevent intestinal epithelial damage.