Peptic ulcers in the gastric tube for esophageal replacement develop in spite of reduction of acid secretion after truncal vagotomy and often result in serious conditions such as bleeding and perforation. Thirteen cases of gastric tube ulcers were detected endoscopically from 1985 to 1990 in our hospital. Most of these ulcers developed within 20 cm of the anastomosis (esophagogastrostomy), which was an especially hypoxic and ischemic area. Ischemic change due to decreased blood supply is suggested as a causative factor in ulcer development. Recent studies indicate that chemiluminescence (ChL) activity may increase even in the low-flow hypoxic condition. Therefore, we investigated the ChL of regional blood in the hypoxic gastric tube in dogs. The ChL activity of the blood sample collected from the ischemic region in the gastric tube significantly increased after construction of the gastric tube, compared with systemic blood from the femoral vein, and the number of leukocytes decreased in the ischemic region. We believe that oxygen radicals derived from neutrophils adhering to the vascular endothelium may play an important role in the damage to endothelial cells of the gastric tube and suggest the possibility of their causative effects in the process of ulcer formations.