There is no generally accepted treatment in the irritable bowel syndrome (IBS), probably because of a lack of convincing therapeutic trials. In the present study, 120 outpatients with IBS participated in a prospective randomized therapeutic trial. According to a double-blind design, 40 patients received 400 mg/day mebeverine and 40 patients received a placebo. In an open branch of the trial, 40 patients were treated with 15 g/day wheat bran. The effects of treatment on symptoms were noted after 4, 8, 12 and 16 weeks of therapy. A significantly superior symptomatic effect of bran in comparison to mebeverine and placebo was demonstrated after 12 weeks, but could not be confirmed at the end of the study. There was no significant difference between the symptomatic effect of mebeverine and placebo. The compliance with the therapy was about 80% for 4 weeks, but dropped to about 50% at the end of the trial. This points to a particular difficulty in the management of patients with IBS. The results of this trial suggest that bran and mebeverine are no ideal therapy for patients with IBS but they support the therapeutic use of bran in patients with IBS.