Eighteen agoraphobic patients were randomly assigned to 12 week treatment with imipramine (I) or imipramine and programmed in-vivo exposure practice (l+BT) to investigate the contribution of behavioural instructions to the clinical effects of pharmacotherapy. Significantly greater improvement on phobic measures was found in the l+BT group compared to the I group. Differences were less marked on measures of panic and anxiety. The results suggest that imipramine possesses an antiphobic effect which can be substantially enhanced with programmed practice. Controlled large-scale investigations of the pharmacological and instructional effects of the pharmacotherapy of agoraphobia are needed for a definitive evaluation of the specific antiphobic effect of antidepressant drugs.