Lactose intolerance and faecal characteristics were compared in 16 patients with symptomatic irritable bowel syndrome and in age- and sex-matched controls. Faecal stool weight was increased in the irritable bowel syndrome patients, whereas faecal bile acids, fat, volatile fatty acids, and neutral sterols were not significantly different. No lactose intolerance was found in irritable bowel syndrome subjects. Measurements of colonic motility showed only modest activity for both basal and food-stimulated activity. There was a weak correlation between the concentration of total bile acids, deoxycholic acid, lithocholic acid and the motility index.