For more than thirty years the pathophysiology of the so-called "irritable bowel syndrome" has given rise to numerous theories. These can be summarized in a series of questions to which this review paper does not pretend to provide definite answers. Is there a basic myoelectric anomaly specific to the irritable bowel syndrome? Are there disorders of colon motility that characterize the symptoms experienced by the patient? Are specific tests available that would stimulate colonic contractions in a reproducible and comparative manner? What place should be given to disturbances in bowel sensitivity? Is the colon the only target-organ in functional intestinal disorders? Is the role of digestive hormones underrated or at least insufficiently known? Do patients with the syndrome have a special psychological profile? Has intolerance to various foodstuffs been excluded too hastily? The secrets of the irritable colon syndrome are far from being entirely unravelled. This heterogeneous group of symptoms seems to be due to many different causes associated to varying degrees in each patient.