Few data have concerned gastric peptic activity in reflux esophagitis. Gastric basal and pentagastrin-stimulated acid, pepsin, sialic acid (marker of gastric mucus erosion) and choline (marker of duodenal refluxate) outputs were measured in 75 patients with gastroesophageal reflux. Fifty-one patients had erosive esophagitis (grade greater than or equal to II) and 24 had no esophagitis or esophagitis grade I. In 12 patients of each group, gastric secretory parameters were correlated with results of 24-hour esophageal pH-metry. Stimulated pepsin output was significantly higher in patients with esophagitis than in the others (P less than 0.001). Basal pepsin output was significantly higher in women with esophagitis than in women without esophagitis (P less than 0.05). Acid, sialic acid, and choline outputs did not differ between the two groups. Thirty-seven and 49 percent of patients with esophagitis had elevated basal and stimulated pepsin outputs, respectively, as compared with 33 and 29 percent of patients without esophagitis. Thirty-one percent of patients with esophagitis had gastric acid hypersecretion, as compared with 25 percent of patients without esophagitis. There was no correlation between gastric secretory parameters and data obtained from esophageal pH-metry. Nevertheless, esophageal acid exposure was higher in patients with esophagitis than in patients without esophagitis. These results suggest that gastric proteolytic content is a pathophysiological factor for erosive esophagitis.