In this study, the ileocecal valve function was evaluated in aspect of prevention of postoperative reflux esophagitis. We have been actively employed ileocolon interposition method for reconstruction following total or proximal gastrectomy since October 1979. Up to September 1983, 24 patients received this operation.Twenty-three patients consuming a house diet had no symptoms of reflux esophagitis.In 21 of 23 patients examined by endoscopy, no esophagitis was found.Manometric study and pH measurement after acid-loading were performed in the interposed ileocolon segment and esophagus in 12 patients under fluoroscopy.According to the analysis of pressure curve and the change of pH value, they were classified into the following four types.Type I (3 cases), high pressure zone (HPZ) is confirmed in the ileocecal junction and pH values change quickly from low to high one in this region.Type II (1 case), HPZ is not clearly observed in the ileocecal junction, but pH curve is similar to that of Type I.Type III (7 cases), neither HPZ nor prompt pH variation was obvious.Type IV (1 case), pressure curve is the same as that of Type I, but pH values do not change at the ileocecal junction.Retching was often noted in each patient, but intraesophageal pH levels were not reduced.Based on these findings, the ileocecal valve appears to have an excellent antireflux function, and we emphasize the usefulness of the ileocolon interposition method to prevent postoperative reflux esophagitis.