We investigated the effect of octylonium bromide on a number of symptoms and functional aspects of the irritable bowel syndrome. Seventy-two patients complaining mainly of abdominal pain were studied in a double-blind trial (octylonium bromide 40 mg tid for 4 weeks or placebo). Clinical parameters were: abdominal pain, bloating and bowel frequency. Sigmoid manometry with simultaneous recording of the thresholds for distension and/or pain upon graded inflation of an endoluminal balloon was performed before and at the end of treatment. In contrast to placebo, octylonium bromide significantly reduced pain and bloating, and significantly increased (p < 0.02) the pain threshold throughout the treatment period. However, comparison with the placebo group failed to show any relevant differences. Neither treatment influenced the frequency of bowel movement. Sigmoid motility during distension was significantly reduced after octylonium bromide (p < 0.05), but it did not change after placebo. In conclusion, octylonium bromide is capable of reducing symptoms and motor reactivity of the sigmoid in patients with irritable bowel syndrome.