The effect of dietary glutamine on bacterial translocation was studied in rats following administration of a single dose of abdominal radiation (1000 rad) that causes a reproducible mucosal injury and results in a high incidence of culture-positive mesenteric lymph nodes after radiation (XRT). Following XRT, rats received only the amino acid glutamine (3%, +GLN) in their drinking water or a control nonessential amino acid (glycine, -GLN). Diets were isonitrogenous and isovolumetric. Four days after XRT, rats were anesthetized and a laparotomy was performed. Mesenteric lymph nodes were sterilely excised and cultured. Arterial blood was also obtained for whole blood glutamine determination. Control rats received no XRT but received identical diets. In XRT rats who received the GLN-free diet, the incidence of culture positive mesenteric lymph nodes was 89% (eight of nine rats) while in the radiated rats receiving the GLN-enriched diet, the incidence fell to 20% (P < 0.05). In non-radiated control rats receiving GLN-enriched and GLN-depleted diets for 4 days, bacterial translocation occurred in zero of eight and one of eight rats, respectively (NS). Provision of glutamine to XRT rats resulted in higher blood levels of glutamine (408 ± 25 μM in XRT +GLN vs 311 ± 19 μM in XRT -GLN, P < 0.05). In addition, provision of GLN maintained mucosal mass and reduced weight loss (P < 0.05). The data lend further support to the hypothesis that glutamine helps maintain the gut mucosal barrier and thereby decreases the incidence of bacterial translocation following bowel injury. The possible mechanisms by which glutamine may reduce the incidence of culture-positive mesenteric lymph nodes following abdominal XRT are discussed. © 1990.