Glutamine may be an essential dietary component, especially for the support of intestinal mucosal growth and function. This study evaluated the effects of a glutamine-enriched elemental diet, administered before whole-abdominal radiation on gut glutamine metabolism, mucosal morphometrics, and bacterial translocation. Rats were randomized to receive a nutritionally complete elemental diet that was glutamine-enriched or glutamine-free for 4 days. The animals were then subjected to a single dose of 1000 cGy x-radiation to the abdomen. After irradiation, all animals received the glutamine-free diet. Four days later the animals underwent laparotomy for sampling of arterial and portal venous blood, culture of mesenteric lymph nodes, and removal of the small intestine for microscopic examination. There was no difference in arterial glutamine or gut glutamine extraction between the two groups, but body weight loss was significantly diminished in the glutamine-fed rats. Rats receiving the glutamine-enriched elemental diet before radiation had a significant increase in jejunal villous number, villous height, and number of metaphase mitoses per crypt. Scanning electron microscopy confirmed the presence of an intact gut epithelium in eight of eight rats receiving prophylactic glutamine compared to one of eight animals in the glutamine-free group. Three of eight rats fed glutamine had culture positive mesenteric lymph nodes compared with five of seven rats receiving the glutamine-free diet. Glutamine exerts a protective effect on the small bowel mucosa by supporting crypt cell proliferation effect on accelerate healing of the acutely radiated bowel.