OBJECTIVE: To compare the efficacy of two doses of lansoprazole with that of placebo in preventing recurrence of erosive esophagitis in a 12-month period. DESIGN: Randomized, double-blind, parallel, placebo-controlled trial. SETTING: 25 U.S. medical centers. PATIENTS: 173 patients with documented healing of erosive esophagitis after 8 weeks of acid-suppressing therapy. INTERVENTION: Lansoprazole, 15 mg or 30 mg, or placebo once daily for as long as 12 months. MEASUREMENTS: Endoscopy and symptom evaluation after 1, 2, 3, 6, 9, and 12 months of treatment. Endoscopy was also done whenever symptoms suggested erosive changes. RESULTS: Lansoprazole was significantly superior to placebo in maintaining healing and preventing recurrence of symptoms. By month 1, 45% of placebo recipients remained healed compared with more than 90% of patients in either lansoprazole group. By month 12, only 24% of placebo recipients remained healed compared with 79% of patients receiving 15 mg of lansoprazole and 90% of patients receiving 30 mg of lansoprazole. During the same period, 35% of placebo recipients remained asymptomatic compared with 72% of recipients of 15 mg of lansoprazole and 67% of recipients of 30 mg of lansoprazole. The 15-mg and 30-mg lansoprazole doses did not differ significantly in maintaining healing and controlling symptoms. Follow-up after recurrence of erosion indicated that during the 12 months, 35% of placebo recipients and 2% of lansoprazole recipients had three or more recurrences. CONCLUSION: Lansoprazole effectively maintains healing of erosive esophagitis. The 15-mg and 30-mg lansoprazole doses did not differ significantly for use as maintenance treatment.