Pirenzepine, a new antimuscarinic drug which selectively binds to gastric mucosal muscarinic receptors, has been found to be as effective as cimetidine in promoting the healing of duodenal ulcer. Since recurrence is the major clinical problem in duodenal ulcer, the authors have performed a double-blind randomized study to evaluate the relapse rates during a follow-up period of six months after healing with pirenzepine. Fifty patients were admitted to the trial and randomly allocated to placebo (group C) or pirenzepine (50 mg daily, group A, and 100 mg daily, group B). Forty-four patients completed the trial. During the six months treatment 9 patients had relapses. No significant difference was found between three groups. No side-effects were observed. The 6-month treatment with 50 mg or 100 mg of pirenzepine was well tolerated and without side-effects. The relapse rate during the six months after healing was very low and no significant difference was found between relapse rates in the three treatment groups. These results suggest that seasonal treatment with pirenzepine will prevent duodenal ulcer relapses, increase patient compliance and reduce the social cost of peptic ulcer disease. Additional studies over 12 months of treatment should be undertaken to verify our findings.