Many factors affect the integrity of transplanted small bowel. These include ischemic preservation and immunologic injury as well as the division of intestinal lymphatics during transplantation. This study was undertaken to evaluate the recovery of fat absorption in transplanted small bowel in syngeneic rats. Orthotopic transplantation of the total small bowel with resection of the native intestine was performed. The experimental (n = 11) and a pair-fed, sham-operated control (n = 8) groups were fed a 50% kcal corn oil semipurified diet. Studies of cyclosporine (CSA) absorption, maltose absorption, dietary fat, and fecal alpha 1-antitrypsin (FA1AT) excretion in transplanted animals were performed preoperatively and at 15, 30, and 50 days postoperatively. There was no significant difference in the weight change or fat and maltose absorption in experimental animals compared with control animals at any time point. Peak serum CSA levels were lower at day 15 in transplanted animals than in controls (P = 0.006) and improved but remained lower than those in controls at days 30 and 50 (P = 0.017). FA1AT excretion was increased on postoperative day 15 (accompanied by a decrease in body weight) and returned to control levels at days 30 and 50. Transplanted isogeneic rats had weight recovery and fat and carbohydrate absorption similar to those of controls. Transplanted animals had a protein-losing enteropathy measured by FA1AT at day 15 that resolved by 30 and 50 days, respectively. CSA absorption showed a much more gradual return to control levels and remained abnormal at 50 days.(ABSTRACT TRUNCATED AT 250 WORDS)