Antral gastrin concentration was measured in endoscopic forceps biopsy specimens and prepyloric mucosa in patients with vagotomy and pyloroplasty, duodenal ulcer patients and nonulcer patients. Antral gastrin concentration in vagotomy and pyloroplasty patients, 35.5 +/- 4.1 ng of gastrin per mg of tissue (mean +/- SEM), was significantly greater (P less than 0.01) than antral gastrin concentration in duodenal ulcer patients, 13.0 +/- 2.4 ng per mg, and antral gastrin concentration in controls, 14.8 +/- 3.1 ng per mg. Basal and meal-stimulated serum gastrin levels in vagotomy and pyloroplasty patients were also significantly greater (P less than 0.05) than gastrin levels in either duodenal ulcer patients or controls. Acid secretion rates were not significantly correlated with serum or antral gastrin concentrations in the patients groups.