Two hundred thirty patients with reflux symptoms and endoscopically proven erosive esophagitis were enrolled from 15 U.S. centers into a randomized, double-blind, dose-ranging study comparing placebo with omeprazole, 20 or 40 mg given once daily in the morning. Esophagitis grade 2 was present in 44% of patients, grade 3 in 37% of patients, and grade 4 in 19% of patients. Endpoints, defined as complete relief of heartburn and complete esophageal mucosal healing, were assessed after 4 and 8 weeks of treatment. Both omeprazole doses were significantly superior to placebo in complete endoscopic healing. After 8 weeks of treatment, 73.5% of patients in the 20-mg omeprazole group and 74.7% in the 40-mg omeprazole group, compared with 14.0% in the placebo group, had complete healing of the esophageal mucosa. At the end of the study, complete relief of daytime heartburn was obtained in 79.5% of patients in the 20-mg omeprazole group, 81.6% in the 40-mg omeprazole group, and 37.2% in the placebo group (P less than or equal to 0.05). Complete relief of nighttime heartburn was noted by 79.5% of patients in the 20-mg omeprazole group, 85.1% in the 40-mg omeprazole group, and 34.9% in the placebo group (P less than or equal to 0.05). The median time to complete relief of daytime and nighttime heartburn occurred earlier in the 40-mg group than in the 20-mg group (9 vs. 17 days and 9 vs. 20 days, respectively); however, these differences were not statistically significant. Relief of acid regurgitation and dysphagia also occurred earlier in the 40-mg group. Omeprazole was well tolerated in this group of patients. No unexpected adverse experiences occurred. The results of this study confirm those of six multicenter, international trials in which omeprazole in doses of 20-60 mg provided a degree of esophageal mucosal healing and complete relief of reflux symptoms superior to any other medical treatment.