OBJECTIVE To date, the effect of Helicobacter pylori on acid secretion remains controversial. To evaluate changes in the gastric acid secretory response before and after H. pylori eradication in a large number of patients, we devised a new endoscopic method of gastric acid secretory testing, the endoscopic gastrin test (EGT). METHODS In EGT, endoscopy was begun 15 min after intramuscular injection of 4 microg/kg tetragastrin. Gastric fluid secreted between 20 and 30 min after gastrin injection was aspirated and collected during endoscopic examination. The amount of acid in the sample collected over this 10-min period was estimated by titration and expressed in H+ mEq/10 min. Fifteen subjects underwent a conventional secretory test using a nasogastric tube (conventional method) and EGT on different days to assess the correlation between results obtained with the two methods. In 10 of these subjects, EGT was repeated under the same conditions to assess its reproducibility. RESULTS EGT values correlated very well with peak acid output determined by the conventional method (n = 15, r = 0.92) and had high reproducibility (n = 10, CV = 5.6). We noted that EGT takes just a little longer to perform than a routine endoscopic examination, and the influence of an endoscope in the stomach on acid secretion was not present. CONCLUSIONS The EGT should be very useful as a rapid, simple substitute for conventional secretory testing when repeated gastric secretory tests are required, especially in investigating the effect of H. pylori on acid secretion in a larger population.