The irritable bowel syndrome (IBS) is part of the spectrum of functional bowel disorders characterised by a diverse consortium of abdominal symptoms including abdominal pain, altered bowel function (bowel frequency and/or constipation), bloating, abdominal distension, the sensation of incomplete evacuation and the increased passage of mucus. It is not surprising therefore that no single, unifying mechanism has as yet been put forward to explain symptom production in IBS. The currently favoured model includes both central and end-organ components which may be combined to create an integrated hypothesis incorporating psychological factors (stress, distress, affective disorder) with end-organ dysfunction (motility disorder, visceral hypersensitivity) possibly aggravated by sub-clinical inflammation as a residuum of an intestinal infection. There is currently no universally effective therapy for IBS. Standard therapy generally involves a symptom-directed approach; anti-diarrhoeal agents for bowel frequency, soluble fibre or laxatives for constipation and smooth muscle relaxants and anti-spasmodics for pain. New drug development has focused predominantly on agents that modify the effects of 5-hydroxytryptamine (5-HT) in the gut, principally the 5-HT(3) receptor antagonists for painful diarrhoea predominant IBS and 5-HT(4) agonists for constipation predominant IBS. More speculative new therapeutic approaches include anti-inflammatory agents, antibiotics, probiotics, antagonists of CCK1 receptors, tachykinins and other novel neuronal receptors.