To examine the long-term management of irritable bowel syndrome we conducted a two-part controlled therapeutic trial on 28 patients who had recovered completely after four to six weeks of treatment with ispaghula husk and propantheline. In part I patients were randomly divided into two groups. Group A received a placebo capsule while Group B continued with treatment as before. After six months the response to treatment was assessed according to a scoring system. The overall relapse rate in Group B was 46 per cent compared to 82 per cent in group A. With continued treatment patients in Group B became asymptomatic from the fourth month while patients in Group A continued to deteriorate. In part II, patients who had relapsed whilst on placebo received active treatment. Six of the seven who agreed to continue with the study became asymptomatic within four weeks. However, all the patients who were asymptomatic while on active treatment relapsed on discontinuation and again recovered on reinstitution of active treatment. We conclude that irritable bowel syndrome is a chronic relapsing disorder and that treatment with a combination of ispaghula husk and propantheline is effective, both in relieving symptoms and in the maintenance of remission.