Calcium polycarbophil was compared with placebo in 23 patients with irritable bowel syndrome in a six-month, randomized double-blind crossover study. Patients received polycarbophil tablets at a dosage of 6 g/day (twelve 0.5-g tablets) or matching placebo tablets. At study end, among patients expressing a preference, 15 of 21 (71%) chose polycarbophil over placebo for relief of the symptoms of irritable bowel syndrome. Statistically significant differences favouring polycarbophil were found among the following patient subgroups: 15 (79%) of 19 with constipation: all six with alternating diarrhoea and constipation; 13 (87%) of 15 with bloating: and 11 (92%) of 12 with two or more symptoms. Polycarbophil was rated better than placebo in monthly global responses to therapy. Patient diary entries showed statistically significant improvement for ease of passage with polycarbophil. Polycarbophil was rated better than placebo for relief of nausea, pain, and bloating. The data suggest that calcium polycarbophil can benefit irritable bowel syndrome patients with constipation or alternating diarrhoea and constipation and may be particularly useful in patients with bloating as a major complaint.