The aim of our study was to demonstrate the effect of Helicobacter pylori eradication on basal and stimulated serum gastrin levels and gastric acid output 5 months after therapy of patients with duodenal ulcer. Thirty-two patients (24 men and eight women with a mean age of 45 years) who had had endoscopy and were diagnosed as having duodenal ulcer entered the study. In all patients three biopsy specimens were taken from the duodenal bulb, gastric antrum, body, and fundus. These specimens were then sent for microbiological and histological examination. Triple therapy consisting of bismuth, metronidazole, and tetracycline was administered. Endoscopy was repeated 1 and 5 months after therapy, and biopsy specimens were again taken from the gastric antrum and body. Before treatment, serum samples were taken to measure basal and stimulated (90 min) gastrin levels after ingestion of two beef cubes, and basal and stimulated acid outputs (after pentagastrin) were studied. Measurements of gastrin and gastric acid output were repeated 5 months after therapy. H. pylori was eradicated in 26 patients (81.3%). Basal gastrin levels (mean +/- SD) at diagnosis and after eradication were 44 +/- 12 and 35.8 +/- 2 pg/ml, respectively (p < 0.05). Similarly, stimulated gastrin levels (integrated values) decreased from 5,303 +/- 1,526 pg/ml/min before therapy to 3,779 +/- 1,204 pg/ml/min after eradication (p < 0.001). However, basal (4.9 +/- 4mEq/h) and stimulated (28.5 +/- 10mEq/h) acid output did not vary after eradication (3.9 +/- 4 mEq/h and 26.2 +/- 12 mEq/h, respectively). We conclude that basal and stimulated gastric acid output are not changed by H. pylori eradication in duodenal ulcer patients 5 months after therapy, in spite of its association with a significant decrease in basal and stimulated gastrin levels.