While on a waiting list for treatment by therapist-guided exposure and ritual prevention (ERP), patients with obsessive-compulsive disorder (OCD) did self-treatment at home guided by a manual plus a computer-driven telephone interview system (BT STEPS). Of 21 patients who used the system for at least three weeks while on the waiting list, one improved so much that subsequent therapist-guided ERP was unnecessary. Progress of the rest with the system predicted later progress with therapist-guided ERP. Improvement after using the system was similar to that of 20 matched historical controls who had had therapist-guided ERP without the prior use of BT STEPS. Outpatient users of BT STEPS needed less subsequent clinician-guided time than did their matched controls. In this pilot study, patients with OCD improved nearly as much with home self-treatment guided by a manual plus computer, as with treatment guided by a behaviour therapist.