Anti-depressants have been reported to be useful in the management of the Irritable Bowel syndrome. We studied the efficacy of amitriptyline for 12 weeks in a randomized double-blind placebocontrolled trial. Forty patients who met predefined criteria entered the trial. They received 25 mg amitriptyline for the first week, 50 mg for the second week and 75 mg nightly thereafter until the end of the 12th week. The drug and placebo groups were comparable in all major pretreatment variables. Amitriptyline was found to be significantly more effective than placebo in producing global improvement, increasing feelings of well-being, reducing abdominal pain and increasing satisfaction with bowel movements. Younger age and increasing extroversion predicted a better response to amitriptyline. Severity of depressive and anxiety symptoms and other personality variables did not influence outcome.