Thirty-six patients, subjected to colon interposition for benign esophageal disease or carcinoma of the esophagus or gastric cardia, were studied by endoscopy for signs of mucosal disease in the interposed colon. Five months to 15 yr (mean 57 months) after the operation, endoscopic finding of the interposed colon was macroscopically normal in 28 patients. Signs of inflammation, including hyperemia or hyperemia and friability, were observed in seven patients. Histologic specimens obtained at endoscopy were examined microscopically, and the findings were compared with those seen in the preoperative graft. In two patients, chronic inflammatory changes were observed in the graft mucosa, consisting of mononuclear cell infiltration of the lamina propria accompanied by crypt dilatation and deformation. In one of these patients, the inflammation was in the proximal third of the graft, and it was also seen at the endoscopy. In the remaining 34 patients, the graft mucosa was microscopically comparable to normal. The alterations were unexpectedly few and mild considering the marked change in the location and function of the colonic segment.