We prospectively studied the use of prophylactic Minnesota antilymphocyte globulin vs. 0KT3 in kidney transplant recipients. Between 7/1/87 and 9/1/90, 138 adult kidney and 35 kidney-pancreas recipients were randomized after stratification for age (18-49 vs. >50), diabetes (diabetic vs. nondiabetic), transplant number (1 vs. >1) and, for retransplants, the length of survival of the first graft (<1 year vs. >1 year), and then randomized to receive 7 days of either MALG (20 mg/kg/day) or OKT3 (5 mg/day). Immunosuppression was otherwise identical in both groups; prednisone and azathi-oprine started on the day of surgery, and cyclosporine started on postoperative day 6. Minimum follow-up was 9 months. There was no difference in one- and two-year actuarial patient or graft survival rates, incidence of rejection, or serum creatinine level. MALG was associated with a higher incidence of cytomegalovirus; it was statistically significant in the subgroup of CMV seronegative recipients of kidneys from seropositive donors (P<.05). OKT3 was more expensive and was associated with significantly more side effects: Fever (P<.0001), dyspnea (P=.04), and acute respiratory distress syndrome (ARDS) (P=.02).