Diarrhea, often profuse, accompanied by skin excoriation and nutritional and electrolyte depletion is a major complication of ileostomy. In an attempt to improve the course of these patients, an experimental study using dogs was undertaken to investigate an antiperistaltic ileal segment for the prevention of ileostomy diarrhea. Ileostomies were created in dogs. All the dogs with ileostomies died within nine days of weight loss and massive electrolyte and water depletion. A second group of animals underwent creation of an ileostomy simultaneously, with an antiperistaltic ileal segment placed 30.5 cm proximal to the ileostomy. These dogs maintained their weight and electrolyte and water balance. The stools in the group with the reversed ileal segment became semisolid to solid, compared to the watery diarrhea of dogs with ileostomies only.