In 40 young patients with chronic renal failure (CRF) on maintenance hemodialysis and 22 control subjects, (1) basal and test meal-stimulated gastrin concentrations, (2) basal and pentagastrin-stimulated gastric acid outputs, and (3) endoscopic examinations were studied. Age-matched CRF patients with control subjects had higher circulating gastrin levels both in the fasting and the test meal-stimulated state and they also had hypochlorhydria. After a test meal, the peak increment of serum gastrin in the CRF patients was more prolonged and greater than in controls. Endoscopic findings showed that the most predominant lesion in the CRF patients was hemorrhagic gastritis. Nine (64.2%) out of 14 patients were hyposecretors and none were hypersecretors. Patients with hyposecretion had higher gastrin levels as well as the same incidence of abnormal endoscopic findings as patients with normosecretion. It is concluded that hypergastrinemia in young CRF patients might be due to a combined effect of impaired renal clearance capacity and overproduction of gastrin associated with hypochlorhydria and also that the cause of gastritis in the young CRF patients might partly be due to a relative impairment of the mucosal defensive mechanism to acid. Our data suggest that the parietal cell response to gastrin in CRF patient may be impaired.