In assessing treatments for chronic diseases such as duodenal ulcer (DU), measuring the patient's quality of life (QoL) is as important as objective measures of treatment efficacy. This study was part of a larger study assessing the QoL of patients with DU treated with nizatidine. The aim of this part of the 12-month study was to assess the clinical efficacy and the influence of maintenance therapy with nizatidine on the long-term treatment of patients with healed DU. The trial, which was open, randomized and controlled, was conducted in 177 centres throughout France. A total of 581 patients of 18 years or over with endoscopically confirmed DU were assigned to two groups. The active treatment group received nizatidine 150 mg/day for one year and the control group had no regular treatment. Both groups had free access to antacid tablets, use of which was recorded. Symptomatic relapse was treated with nizatidine 300 mg/day for 6 weeks. Clinical assessments were made every 2 months, at which times patients also recorded their symptoms. The relapse rate in the nizatidine-treated group was significantly lower than in the control group at 6 months (4.5% versus 15.3%; p < 0.0001). At 12 months the difference was still significant (8.0% versus 33.5%; p < 0.001). Antacid consumption was significantly greater in controls than in the nizatidine-treated group (44.7% versus 29.7%; p < 0.001). It is concluded that nizatidine is a safe and effective therapy for preventing DU recurrence in patients with endoscopically confirmed healed ulcers.