An intraluminal sphincter was constructed by invagination of an everted portion of the distal small intestinal segment into the proximal intestinal segment in nine dogs after 80% distal small intestinal resection. Six dogs with similar resections but no artificial sphincters were used as controls. If the invaginated portion was uniform and at least 1 cm in depth, intestinal transit was retarded. Ability to slow the loss of body weight was related to the competence of the sphincter. Use of the sphincter to retard bowel transit was not without complications: (a) Gastric ulcers developed in some dogs and occult blood was found in the stool. (b) Secondary anemia occurred. (c) Steatorrhea was intensified. It was thought to be due to excessive bacterial proliferation from colonic reflux and stasis proximal and distal to the sphincter.