The mechanism of acute gastric ulcerations in rats with obstructive jaundice was investigated in terms of the changes in the gastric mucosal blood flow. Further, the effect of vagotomy with or without obstructive jaundice was examined. One hundred and eighty-eight Sprague-Dawley rats weighing about 250 g were prepared and divided into 4 groups as follows; sham operation (control group), ligation of the bile duct (jaundiced group), vagotomy with pyloroplasty (vagotomized group), ligation of the bile duct and vagotomy with pyloroplasty (jaundiced and vagotomized group). After two weeks, water immersion and restraint stress procedures were performed in these 4 groups. The gravity of the gastric ulcerations was calculated by ulcer index. The gastric mucosal blood flow was measured by hydrogen clearance technique. The following results were obtained. The control group showed increased ulcer index and decreased gastric mucosal blood flow after the stress procedures. The jaundiced group showed significantly higher ulcer index and early, significant decrease of gastric mucosal blood flow compared to the control group after the stress procedures. The vagotomized group showed significantly decreased ulcer index after stress procedures compared to the control group, however, the gastric mucosal blood flow were unchanged between both groups before and after the stress procedures. The jaundiced and vagotomized group showed significant decrease of ulcer index and improvement of decrease of gastric mucosal blood flow compared to the jaundiced group. These data suggested that the significant decrease of gastric mucosal blood flow during the stress procedures was one of exacerbating factors of the acute gastric ulcerations in rats with obstructive jaundice, and vagotomy might prevent them by maintaining the gastric mucosal blood flow in obstructive jaundice.