This multicenter, randomized, double-blind, 8-wk study compared the new H+/K(+)-ATPase inhibitor, lansoprazole, 30 mg daily, to ranitidine 150 mg bid for treatment of erosive reflux esophagitis resistant to histamine-2 receptor antagonists (H2RA). Patients were evaluated after 2, 4, 6, and 8 wk of treatment by symptom assessment and endoscopy. Healing rates for lansoprazole were 71%, 80%, 88%, and 89% at 2, 4, 6, and 8 wk, respectively, compared to 21%, 33%, 45%, and 38% for ranitidine (p < 0.001 at all points). Lansoprazole was significantly more effective than ranitidine for relief of heartburn and reduction of antacid tablet use. Increases in serum gastrin concentrations between the baseline and the 8-wk visit were greater in lansoprazole-treated than in ranitidine-treated patients. Lansoprazole was safe and well tolerated. In patients with erosive reflux esophagitis resistant to standard doses of H2RA, lansoprazole 30 mg/day is more effective than continuation of an H2RA (ranitidine 150 mg bid) for healing of esophagitis and improvement of symptoms.