Extrinsic denervation and lymphatic disruption impair nutrient absorption after small bowel transplantation. The present study was undertaken to determine whether adding the ileocecal valve with or without the ascending colon would improve the function of a segmental intestinal graft. Five groups of Lewis rats (n = 10/group) were studied. Group I had a sham laparotomy. Groups II, III, IV, and V had the native jejunum, ileum, and cecum replaced with a graft. Inbred Lewis rats were used as isogeneic donors for the transplants to avoid the confounding effect of graft rejection. Group II had the entire jejunum and ileum transplanted. Group III had 20 cm of terminal ileum transplanted. Group IV had 20 cm of the terminal ileum including the ileocecal valve transplanted. Group V had 20 cm of the terminal ileum, the ileocecal valve, and the ascending colon transplanted. The terminal ileum-transplanted and terminal ileum/ileocecal valve-transplanted groups lost more than 25% of their preoperative weight by the end of the second postoperative week; most of these animals were killed because of inanition. In contrast, the sham laparotomy, jejunum/ileum-transplanted, and ascending colon-transplanted groups remained healthy until completion of the study on the 28th postoperative day. The ascending colon-transplanted group had slower intestinal transit and less bacterial contamination of the terminal ileum compared with the terminal ileum-transplanted and terminal ileum/ileocecal valve-transplanted groups (P < 0.05). Transplantation of the ascending colon and the ileocecal valve significantly improves the function of segmental small bowel isografts in rats. These data suggest that adding a colonic segment may be a simple method to improve the function of short-segment cadaveric and living-related intestinal grafts in humans.