In an open prospective parallel group multicentre study, 54 patients with irritable bowel syndrome were randomised to receive oral mebeverine slow release 200mg twice daily (n = 26) or mebeverine tablets 135mg 3 times daily (n = 28) for 3 weeks. Eight gastrointestinal symptoms and 3 nongastrointestinal symptoms were evaluated. The analysis of the data did not demonstrate a difference in efficacy between the treatment groups. Both mebeverine preparations, the tablet and the new slow release formulation in microgranules, were found to be safe and well tolerated. Of the 54 patients who entered the study, 6 discontinued medication prematurely, and 48 were included in the final analysis. Systolic and diastolic blood pressure and pulse rate did not show a significant change over time nor a difference between groups. No serious adverse drug event was reported. The investigator's global impression of compliance after 1 and 3 weeks of treatment did not show a significant difference between treatment groups. The idea of reducing the number of daily doses from 3 to 2 by using a slow-release formulation was confirmed in this study.