In the course of extensive routine screening for bile acid malabsorption a few patients were detected in whom chronic diarrhoea was apparently induced by excess bile acid loss which was neither associated with demonstrable conventional ileopathy nor with any other disorder allied to diarrhoea. In three patients subjected to scrutiny the results obtained were in harmony with a concept of idiopathic bile acid catharsis. Ingestion of cholestyramine was followed by immediate relief, but the diarrhoea recurred whenever this treatment was withdrawn. It it suggested that idiopathic bile acid catharsis should be suspected in patients with unexplained chronic diarrhoea and especially in those with a diagnosis of irritable colon with diarrhoea.