Forty-two patients with peptic ulceration of the duodenum, stomach or oesophagus, who had not responded to 3 or more months of high-dose treatment with ranitidine (450 or 600 mg/day), were treated with oral lansoprazole at 30-60 mg daily. In 40 patients (95.2%) the ulcers healed within 2-12 weeks. In the remaining 2 patients healing took several months but eventually all ulcers healed. After healing, 40 patients underwent long-term maintenance treatment with 30-60 mg lansoprazole daily for 1-3 years (continuing). During maintenance therapy with lansoprazole, no endoscopically verified relapses occurred when the drug was taken regularly. In 1 patient treatment had to be discontinued because of a drug-related colitis that disappeared soon after treatment had been stopped. There were no significant changes in routine laboratory tests in any patient. Basal serum gastrin concentrations, which were already elevated by the previous high-dose ranitidine treatment (125 +/- 25 pg/ml), rose to four times the normal values after 4 weeks of treatment with lansoprazole (255 +/- 65 pg/ml). Thereafter no further increases in basal serum gastrin concentrations were observed, even after 3 years of administration. The volume density of argyrophilic cells in the oxyntic mucosa increased slightly during lansoprazole treatment; until now no dysplasia of the enterochromaffin-like cells has been observed. In conclusion, 30-60 mg lansoprazole daily healed ranitidine-resistant peptic ulcers, and subsequent maintenance therapy with 30-60 mg lansoprazole daily was found to be highly effective and safe over the time observed.