How bad are the symptoms and bowel dysfunction of patients with the irritable bowel syndrome? A prospective, controlled study with emphasis on stool form. Since it is not known whether the symptoms and bowel function of patients with the irritable bowel syndrome are truly abnormal we used diaries and frequent telephone interviews over a 31 day period to assess symptoms, defecation, and stool types in 26 unselected female hospital patients with the irritable bowel syndrome, 27 women who admitted to recurrent colonic pain but had not consulted a doctor (non-complainers), and 27 healthy control subjects. Unexpectedly, abdominal pain and bloating occurred in most of the control subjects. Pain, however, was six times more frequent in the patients and was more often considered severe. Bloating occurred three times more often. Defecation was more frequent, more erratic in timing and stool form, and more likely to produce stools of extreme forms, indicating rapid fluctuations in intestinal transit time. Urgency was four times more prevalent in patients than control subjects. Straining to finish defecating was nine times more prevalent and was often accompanied by feelings of incomplete evacuation--a combination which could lead to the misdiagnosis of constipation. The normal relation between stool form and the above symptoms was distorted, possibly due to rectal irritability. Non-complainers were intermediate between patients and control subjects in almost every parameter but were closer to control subjects than to patients. Patients with the irritable bowel syndrome have real cause for complaint and their bowel function is truly abnormal. 