Although reflux esophagitis after subtotal gastrectomy has been noticed by surgeons, the mechanism of its development is obscure. This study was undertaken with the aim of clarifying the role of the lower esophageal sphincter in the development of this abnormality. Manometric studies were carried out on 42 patients with gastric cancer, and on 19 with cholelithiasis. The lower esophageal sphincter pressure was measured using a catheter tip pressure transducer and a rapid pull-through technique, and the results presented as the mean of three measurements. The technical error of this experiment was estimated to be within 2 mmHg by a study of the cholecystectomy patients. After gastrectomy, the lower esophageal pressure decreased in 17 patients, increased in 4 and remained unchanged in 21. A more pronounced decrease in the lower esophageal sphincter pressure was found after Billroth II. Clinical evaluation of the 42 patients revealed symptoms of postgastrectomy regurgitation in 10. Preoperatively, these 10 had lower values of the lower esophageal sphincter pressure followed by a more marked postoperative decrease, as compared with the patients with no regurgitation symptoms. Oral administration of a test meal revealed regurgitation after subtotal gastrectomy. This study suggests that a low value of the pre-operative lower esophageal sphincter pressure, a marked decrease in the pressure after gastrectomy, and Billroth II anastomosis, may be factors that predispose to regurgitation.