Because of a sharp increase in the number of permanent pacemakers inserted at The Brooklyn Hospital between 1972 and 1976, a peer-review committee was established to monitor subsequent pacemaker implantation. Total initial implants declined from 48 to 22 per year in the two years that followed. The number of implantations for sinoatrial bradycardias declined from 50 to 27 and the number of implantations for intraventricular conduction defects declined from 32 to five in the two years after peer review, compared with the two years before. There was no change in the number of pacemakers implanted for complete or advanced heart block. Almost 10% of patients who received a pacemaker between 1972 and 1976 had other conditions that might have accounted for the events that precipitated the decision to implant a pacemaker. The symptoms for which the pacemaker was implanted persisted in 19% of patients, despite a normally functioning pacemaker system. Patients receiving a permanent pacemaker before peer review had a 17% one-year and a 43% three-year mortality. When a more critical patient selection process was instituted, a smaller percentage remained symptomatic (9% vs 19%) and three-year survival rate was improved (86% vs 57%). From 1977 through 1978, when permanent pacemaker implantations declined, the number of hospital, medical service, and coronary care unit admissions increased. It is concluded that peer review can have substantial impact on permanent pacemaker implantations.