The objective of this study was to determine whether supplemental glutamine (alanylglutamine dipeptide) is effective in preventing small intestinal mucosal atrophy associated with total parenteral nutrition and whether it affects the growth of other organs in neonatal pigs. We compared organ growth, intestinal enzyme activity, and plasma nitrogen metabolites in 4-day-old pigs randomly selected to receive total parenteral nutrition supplemented with 0 g, 2.0 g, or 4.5 g of glutamine per deciliter for a total amino acid intake of either 11 or 25 g.kg-1.d-1 for 7 days. Glutamine supplementation increased (60% to 100%) plasma concentrations of glutamine, urea nitrogen, ammonia, and both jejunal villus height and surface area, but it did not significantly affect jejunal mucosal protein and DNA masses or the relative growth of liver, kidneys, and brain. No histologic evidence of tissue toxicity was found. Supplementing large amounts of glutamine (alanylglutamine dipeptide) did not completely prevent total parenteral nutrition-associated intestinal mucosal atrophy but did improve villus morphology without affecting vital organ growth or histology.