Thirty-nine heart transplant recipients were randomized prospectively to receive OKT3 or antilymphoblast globulin (ALG) for 7 days, having otherwise identical protocols (group 1: OKT3, n = 20 patients; group 2: ALG, n = 19 patients). No preoperative immunosuppression was given. The protocol consisted of methylprednisolone, 500 mg intraoperatively, followed by 1 mg/kg/day, intravenously or orally, tapering to 0.2 mg/kg/day at 1 month; oral cyclosporine starting 3 to 5 days after transplantation; selective use of azathioprine, 1 to 4 mg/kg/day; and either OKT3, 5 mg/day for 7 days, or ALG, 15 mg/kg/day for 7 days. Of the 39 patients in the study, 34 are alive 6 months to 2 years after transplantation. The actuarial survival at 2 years for the OKT3 and ALG groups was 92% (+/- 0.07%) and 83% (+/- 0.09%), respectively (not significant [NS]). The time to first rejection for group 1 was 5.6 weeks and for group 2 was 5.3 weeks (NS). The mean number of rejections for group 1 and group 2 was 2.1 episodes per patient and 1.4 per patient, respectively (NS). Three patients in each group were free of rejection at 6 months. The total number of infections at 6 months was 1.05 per patient in group 1, 0.74 per patient in group 2 (NS), with 35% of patients receiving OKT3 and 52% of patients receiving ALG actuarially free of infection by 6 months after surgery (NS). During the first 24 hours after surgery, no significant differences were noted in mean blood pressure, central venous pressure, or Po2 between the groups.(ABSTRACT TRUNCATED AT 250 WORDS)