Duodenal gastrin concentration was measured in endoscopic forceps biopsy specimens of the juxta-pyloric duodenal mucosa in patients with various gastrointestinal disorders. Duodenal gastrin concentration was 5.9 +/- 1.2 ng/mg (mean +/- 1 SEM) in control patients. Duodenal gastrin concentration was similar to control values in patients with duodenal ulcer, pyloric channel ulcer, vagotomy and pyloroplasty, and gastric atrophy and hypergastrinemia. In gastric ulcer patients, duodenal gastrin concentration, 2.8 +/- 0.6 ng/mg, was significantly less than the control value (P less than 0.05). Duodenal gastrin concentration was approximately one third of antral gastrin concentration in control, duodenal ulcer, and gastric ulcer patients and was approximately one fifth of antral gastrin concentration in vagotomy and pyloroplasty patients and gastric atrophy patients. Duodenal and antral gastrin concentrations were significantly correlated in normal controls and in gastric ulcer patients. The finding of normal duodenal gastrin concentration in patients with vagotomy and pyloroplasty and patients with gastric atrophy suggests that, unlike antral gastrin concentration, duodenal gastrin concentration is unaffected by a decrease in acid secretion rate. The low duodenal gastrin concentration in gastric ulcer patients indicates that the duodenum may be involved in the pathophysiology of gastric ulcer disease.