OBJECTIVE To study the role of autonomic nervous innervation in the etiology of peptic ulcer, we investigated the blood pressure in patients with peptic ulcer. METHODS In 100,085 Japanese adults who were undergoing health screening examinations, including barium meal study, there were endoscopic evaluation-confirmed diagnoses of gastric ulcer in 769 cases and of duodenal ulcer in 344 cases. The blood pressure in those patients was compared with that in 57,208 normal Japanese controls with no gastrointestinal abnormalities, as confirmed by barium meal study. RESULTS The blood pressure of younger and middle-aged men with gastric and duodenal ulcer were lower than those of normal control men. In women, except for the diastolic pressure of those in their 50s, the blood pressure in patients with peptic ulcer and normal controls did not differ significantly. The incidence of duodenal ulcer or of gastric ulcer in men was inversely related to the systolic and diastolic pressure. No definite relationship in this respect was seen in women. CONCLUSIONS An inverse relationship was observed between the occurrence of peptic ulcer and the blood pressure level in Japanese men, but not in women. The relationship may be mediated by an inhibitory effect of the sympathetic nervous system on ulcer formation in hypertensive subjects. The reason for the sex difference in this respect is unknown.