Aim: To identify an appropriate dose of renzapride (a 5-HT(4) receptor full agonist/5-HT(3) receptor antagonist) to treat abdominal pain/discomfort in patients with IBS-C. Methods: In this randomised, placebo-controlled, phase IIb study in the primary care setting, men and women were randomised to placebo or renzapride (1, 2 or 4 mg/day) for 12 weeks. The primary outcome measure was patient self-assessed relief of abdominal pain/discomfort during Weeks 5-12. Secondary efficacy measures included patients' assessment of their bowel habits, stool consistency, and quality of life. Results: Although there were no statistically significant differences between renzapride and placebo for relief from abdominal pain/discomfort, responder rates in the renzapride treatment groups increased dose-dependently, with the 4 mg/day group being consistently numerically greater than placebo. Importantly, a larger numerical treatment difference versus placebo was observed in women (7.7% and 12.3%, respectively). Statistically significant improvements in bowel movement frequency and stool consistency were observed in the 4 mg/day group relative to placebo. Renzapride was well tolerated at all doses. Conclusions: This study confirms the potent GI prokinetic effects of renzparide. The data also suggested a potentially beneficial effect on abdominal pain/discomfort in women with IBS-C.