Liquid elemental diets are associated with mucosal hypoplasia of both the small intestine and colon. Neurotensin, a tridecapeptide widely distributed in the gut, is trophic for the small intestine of rats fed a normal chow diet. The purpose of this study was to determine whether neurotensin could reverse the hypoplasia of intestinal mucosa that is associated with feeding a liquid elemental diet. Forty male Sprague-Dawley rats were randomized into five groups. Four groups were fed (for seven days) a glutamine-free liquid elemental diet. Subcutaneous injection of saline (control) or neurotensin (33, 100 or 300 micrograms/kg) were given to the groups of rats every 8 hr for seven days. Group five (Chow) received rat chow ad libitum for seven days. Rats were killed on day 8, and the proximal jejunum, distal ileum, and proximal colon removed. Mucosal weight, DNA, RNA, and protein contents were determined. Neurotensin (300 micrograms/kg) increased the cellularity of the small intestinal mucosa and reversed mucosal hypoplasia due to an elemental diet; a more pronounced effect was noted in the jejunum compared to the ileum. Neurotensin (33 and 100 micrograms/kg) increased mucosal DNA content in the jejunum but was not effective in reversing the hypoplasia. Neurotensin had no effect on growth of colonic mucosa. These results suggest that neurotensin may be an important trophic hormone for the small intestine. Administration of neurotensin may alleviate hypoplasia of the small bowel mucosa and maintain functional integrity of the gut during prolonged feeding of an elemental diet.