A six-week trial of 300 mg clomipramine hydrochloride (Anafranil, Geigy Pharmaceuticals) was compared to a six-month twice weekly therapeutic programme with two widely used behavioural techniques, flooding and thought-stopping. Clomipramine had a substantial ameliorating effect on the number and severity of obsessional symptoms, reducing the total obsessive symptomatology by half. The trends suggested that the drug was as effective as flooding and more effective than thought-stopping in reducing the ruminative symptoms, and was especially effective in reducing pervading doubt. It was considerably less effective than behaviour therapy in reducing the compulsive symptoms. This suggests, and confirms the authors' clinical impression, that a combination of pharmacotherapy and behaviour therapy is the optimal treatment of choice for ritualistic patients who are almost always very ruinative, doubtful and highly anxious. Clomipramine had the most substantial anxiolytic effect of three groups and seemed to be as effective as behaviour therapy in reducing phobias.