Bacterial flora, activities of 10 potential mucus- and dietary polysaccharide-degrading enzymes, blood group antigenicity of the intestinal glycoproteins, and proteolytic activity in the output from experimentally colectomized dogs with conventional ileostomies and dogs with valveless ileal reservoirs (pouches) were determined. The ileostomies of dogs with conventional surgery (group II) and with pouches (group III) were occluded intermittently during a 6-week period. The duration of occlusion was progressively increased. Group I, five dogs with conventional ileostomies, served as a control group. After occlusion of the ileal pouch for 7 h, total numbers of bacteria increased threefold, glycosidase activity increased fivefold, and blood group antigenicity of the intestinal glycoproteins, which was high in the output from the nonoccluded pouch, was no longer detectable. Proteolytic activity was not influenced by occlusion of the pouch. Significantly lower numbers of bacteria, only minor glycosidase activity, high blood group antigenicities of the intestinal glycoproteins, and higher proteolytic activity were found in ileostomy effluents from groups I and II. Histopathological examination showed chronic inflammation and changes in crypt-villus ratio in all dogs with ileal reservoirs; the ileal mucosa from the dogs with conventional ileostomies did not show any abnormalities. Consequences of the flora-related enzyme activities for the ileal mucosa are discussed.