Dogs having a jejunoileal bypass, with the distal end of the bypassed segment being exteriorized as an ileal stoma, were compared with a control group having a Payne type jejunoileal bypass. In both groups, approximately 83 percent of the small intestine was bypassed. All except one dog survived the full six months of the study. During the first four months after the jejunoileal bypass, the dogs having an ileal stoma had more stable food consumption, less weight loss and higher levels of serum albumin than did those of the control group. During this period the bypassed segment in dogs of the control group usually contained bacteroides, whereas, after ileostomy, the segments were usually free of these organisms. At six months after jejunoileal bypass, there was no significant difference in the two groups with regard to nutrition, weight and the presence of bacteroides in the excluded segment. The hepatic structure and function was unaffected by both bypass procedures. Following a jejunoileal bypass in the dog, the complications associated with the excluded segment can be lessened by exteriorizing the distal end of the segment as a cutaneous ileal stoma.