Résumé : Maximal acid outputs were determined during intravenous pentagastrin tests (6 μg/kg/h) in 119 male subjects: 17 controls, 74 patients with duodenal ulcer and 28 with atrophic gastritis. Basal and postprandial serum gastrin levels were also determined in order to estimate the integrated gastrin response to the meal. In patients with atrophic gastritis the maximal acid output was decreased (p < 0.01) and the integrated gastric response was increased (p < 0.01) but the basal gastrin levels in these patients did not differ from that of controls. An integrated gastrin response greater than 2.5 ng/ml/100 min was observed in 89% of patients with atrophic gastritis. An integrated gastrin response smaller than 2.5 ng/ml/100 min was observed in 76% of controls. The maximal acid output was smaller than 20 mmol/l in all patients with atrophic gastritis but was greater than this value in all controls. In duodenal ulcer patients, the measured parameters were not significantly different from control values. The measure of the integrated gastrin response which reflects the presence of antral endocrine hyperactivity may be useful to detect patients with atrophic gastritis, but this test is less sensitive and less specific than the determination of the maximal acid output.