In order to obtain criteria characteristic of the irritable bowel syndrome (IBS), the authors sent out questionnaires to evaluate the bowel habits and intestinal disorders in patients with IBS and to identify and compare clinical findings with patients who had other gastroenterology pathology. In this article, we discuss the results of this survey conducted in the United States, its clinical consequences and its value in identifying characteristics of patients with the IBS. In 94.2 percent of the population studied (students and employees at the North Carolina University Hospital), stool frequency ranged from 3 per week to 3 per day. Variations were dependent on the race and sex of patients: men had more frequent bowel movements than women (9.2 vs 6.7 per week; p less than 0.0001), and Caucasians had more frequent bowel movements than Blacks (7.8 vs 6.0 per week; p less than 0.0001). Definitions of constipation and diarrhea vary, which shows that the manner in which questions are asked is very important in surveys on intestinal disorders. Symptoms suggesting IBS were found in 15 to 17 percent of cases. The group of subjects with IBS: a) were mostly women (72.6 vs 54.4 percent), b) considered that psychologic stress was a cause of intestinal disorders (84.4 vs 67.6 percent) and intestinal incomfort (68.9 vs 48.0 percent), and c) used laxatives more than once a month (12.6 vs 1.5 percent). The majority of patients (62 to 77 percent) without symptoms of IBS had never sought medical advice before for their symptoms.(ABSTRACT TRUNCATED AT 250 WORDS)