OBJECTIVES: Esomeprazole, the S isomer of omeprazole, has been shown to have higher healing rates of erosive esophagitis than omeprazole. This study compared esomeprazole with lansoprazole for the healing of erosive esophagitis and resolution of heartburn. METHODS: This United States multicenter, randomized, double blind, parallel group trial was performed in 5241 adult patients (intent-to-treat population) with endoscopically documented erosive esophagitis, which was graded by severity at baseline (Los Angeles classification). Patients received 40 mg of esomeprazole (n = 2624) or 30 mg of lansoprazole (n = 2617) once daily before breakfast for up to 8 wk. The primary efficacy endpoint was healing of erosive esophagitis at week 8. Secondary assessments included proportion of patients healed at week 4, resolution of investigator-recorded heartburn, time to first and time to sustained resolution of patient diary-recorded heartburn, and proportion of heartburn-free days and nights. RESULTS: Esomeprazole (40 mg) demonstrated significantly higher healing rates (92.6%, 95% CI = 91.5-93.6%) than lansoprazole (30 mg) (88.8%, 95% CI = 87.5-90.0%) at week 8 (p = 0.0001, life-table estimates, intent-to-treat analysis). A significant difference in healing rates favoring esomeprazole was also observed at week 4. The difference in healing rates between esomeprazole and lansoprazole increased as baseline severity of erosive esophagitis increased. Sustained resolution of heartburn occurred faster and in more patients treated with esomeprazole. Sustained resolution of nocturnal heartburn also occurred faster with esomeprazole. Both treatments were well tolerated. CONCLUSIONS: Esomeprazole (40 mg) is more effective than lansoprazole (30 mg) in healing erosive esophagitis and resolving heartburn. Healing rates are consistently high with esomeprazole, irrespective of baseline disease severity.