In most patients duodenal ulcer is a chronicrelapsing disease. If no active maintenance treatment oreradication therapy is given after healing, around70-100% of patients have a relapse during the first year. We conducted a double-blind multicenterstudy in 472 patients with duodenal ulcer. They weretreated with omeprazole 20 mg every morning for four oreight weeks and when healed were randomly allocated to maintenance treatment with either omeprazole20 mg every morning or ranitidine 150 mg at bedtime forup to six months. The patients were assessed byendoscopy at monthly intervals until healing occurred. Thereafter scheduled endoscopy was carried outafter 1, 3, and 6 months of maintenance treatment orimmediately in the event of a suspected relapse. Healingstatus (intention to treat approach) was 87% at four weeks and 93% at eight weeks. At sixmonths the estimated remission rate was 90% foromeprazole and 82% for ranitidine (P = 0.03, 95% CI1-15%). The incidence of adverse events was similarduring the two maintenance treatments. Treatment withomeprazole 20 mg every morning maintained significantlymore patients in remission than treatment withranitidine 150 mg at bedtime.