One hundred two patients with irritable bowel syndrome were studied in a controlled trial of psychological treatment involving psychotherapy, relaxation, and standard medical treatment compared with standard medical treatment alone. Patients were only selected if their symptoms had not improved with standard medical treatment over the previous 6 months. At 3 months, the treatment group showed significantly greater improvement than the controls on both gastroenterologists' and patients' ratings of diarrhea and abdominal pain, but constipation changed little. Good prognostic factors included overt psychiatric symptoms and intermittent pain exacerbated by stress, whereas those with constant abdominal pain were helped little by this treatment. This study has demonstrated that psychological treatment is feasible and effective in two thirds of those patients with irritable bowel syndrome who do not respond to standard medical treatment.