Antral gastrin concentration (AGC) was measured in prepyloric mucosa specimens obtained by forceps biopsy during endoscopic examination of 174 clinic and hospital patients. AGC in 32 patients who had normal endoscopic findings, the control group, varied widely from 2 to 38.6 ng gastrin/mg tissue. The mean AGC of the control patients was 14.2 +/- 1.4 (mean +/- 1 SE) ng gastrin/mg tissue. AGC was similar to control values in 18 patients with duodenal ulcer, 14.7 +/- 2.1; 12 patients with a pyloric channel or antral ulcer, 16.4 +/- 3.5; and 48 patients with miscellaneous diagnoses, 14.3 +/- 1.5. AGC was significantly less than control values in 13 patients with a ulcer in the body or fundus of the stomach, 5.9 +/- 1.5, and 4 patients with the Zollinger-Ellison syndrome, 4.9 +/- 2.4. AGC was significantly greater than in control values in 16 patients with gastritis, 25.8 +/- 4.3;22 patients with esophagitis, 23.2 +/- 3.0; and 9 patients with gastric atrophy and fasting serum hypergastrinemia 44.6 +/- 12.3. In group of 77 of these patients with heterogeneous diagnoses, meal-stimulated 3-hr integrated gastrin output was directly related to AGC (r = 0.47, P less than 0.001). In a group of 106 patients AGC was inversely related to histalogstimulated maximum acid output. The correlation was very weak (r = -0.20) but significant (P less than 0.05).