The motor activity of the canine lower esophageal sphincter (LES) was studied under conscious states by means of the strain gage transducer, and gastroesophageal reflux was investigated after injection of the contrast medium through the silastic tube inserted in gastric fundus by x-ray. The motor activity and function of LES were observed in the dogs with selective proximal vagotomy (SPV), truncal vagotomy (TV) and TV + gastrectomy. Results were summarized as follows; 1. In the postprandial period, so called receptive relaxation was observed in gastric body, and tonic contraction was observed in LES. On the other hand, the occurrence of the LES contraction was consistent with gastric periodic motor activity in the interdigestive state. It was found that such a contractile pattern of LES and gastric body prevented the reflux of gastric juice from stomach to esophagus in the digestive and interdigestive state. 2. In the postprandial period, the tonic contraction of LES was inhibited by the venous injection of atropine sulfate. Mechanisms of digestive contractile activity of LES were mainly regulated by cholinergic nerve. 3. After SPV and TV, the motility of LES and gastric body was disturbed. Namely, receptive relaxation disappeared, and tonic contraction was observed in gastric body, but the relaxation of the LES was found after ingestion. These findings suggested that discordant LES contractiles with the contraction of the gastric body after vagotomy produced a gastroesophageal reflux. 4. After TV + gastrectomy, the synchronous motor activity of the LES, remnant stomach and duodenum disappeared. Namely, it was thought that the reflux esophagitis occurred after gastric surgery with vagotomy and lymphnodes dissection was caused by the duodenal juice reflux to remnant stomach and esophagus.