Fifty-four patients with endoscopically documented therapy-resistant erosive reflux esophagitis were treated with lansoprazole, a new proton pump inhibitor, for up to 12 weeks. Prior to entry, all had remained unhealed after treatment with at least two histamine2-receptor antagonists, at therapeutic doses or higher, for at least 12 weeks. Patients were randomized to receive either 30 or 60 mg lansoprazole once daily. Endoscopy was performed and symptoms assessed at weeks 2,4,6,8 and 12. Fifty-nine percent of the 50 evaluable patients were healed (ie, no evidence of erosions) after only two weeks of lansoprazole. Cumulative endoscopic healing rates were 82% and 92% by week 4 and week 8, respectively, and the two doses were equally effective in healing. The 30- and 60-mg doses effected a decrease in the overall symptom score from 5.30 and 4.85 to 2.35 and 1.67, respectively, by the final treatment visit (P = 0.001). No clinically significant adverse events or changes in laboratory parameters were observed, and no patients withdrew prematurely from the study. This study demonstrates that lansoprazole therapy is highly effective in healing erosive reflux esophagitis resistant to therapy with histamine H2-receptor antagonists.