The purpose of this study was to review our experience with the use of OKT3 (a murine monoclonal CD3 antibody) used as immune prophylaxis for pediatric heart transplant recipients. Orthotopic heart transplantation was performed in 18 pediatric patients, 8 girls and 10 boys, ranging in age from 17 days to 17 years. OKT3 therapy was initiated intraoperatively at a dose of approximately 0.2 mg/kg and was administered at a dose of approximately 0.1 to 0.2 mg/kg/day for a period of 11.5 +/- 2.5 days. Daily average OKT3 levels were 1132 +/- 469 ng/ml. Side effects that occurred during OKT3 therapy were fever (59%), diarrhea (24%), headaches (24%), vomiting (18%), encephalopathy (12%), pulmonary edema (6%), and rash (6%). Infections occurred in 24% of patients, all within 6 months of transplantation. In the first year after transplantation, patients experienced 3.4 +/- 2.4 episodes of mild rejection and 1.0 +/- 0.8 episodes of moderate rejection. No patient experienced severe rejection. Five of the surviving 14 patients (36%) have been weaned from chronic steroid therapy, and 42% are being maintained on alternate-day prednisone at a dose of 0.06 +/- 0.02 mg/kg/day. Coronary artery disease developed in three patients; two of whom died. Actuarial survival was 83% at 1 year and 73% at 2 years. This report shows that OKT3 prophylaxis in pediatric heart transplantation can be used with acceptable short-term adverse side effects and overall survival.