The effect of cyclosporine and steroids on early renal allograft function and eventual graft outcome was analyzed in 100 recipients; 33 recipients of living related donor (LRD) and 67 recipients of cadaveric donor (CAD) allografts were studied. A concurrent population of 47 CAD recipients treated with azathioprine and steroids was used for comparison. Recipients received oral cyclosporine (14 mg/kg) 48 hours (LRD) or 6–l2 hours (CAD) pretransplant. No cases of acute tubular necrosis (ATN) were observed in the LRD recipients. The incidence of posttransplant ATN was similar in the cyclosporine-treated (41%) and in the azathioprine-treated (45%) CAD recipients (P = ns). Cyclosporine-treated CAD kidneys preserved less than 24 hr experienced a lower rate of ATN (P <.01) using simple cold storage (31%), as compared with hypothermic pulsatile perfusion (57%). One-month creatinine nadirs were higher in cyclosporine-treated than in azathioprine-treated recipients, using median values for each group. One-year actuarial patient survival for cyclosporine-treated LRD recipients was 97%; CAD recipients, 94%, and azathioprine-treated CAD recipients, 91%. Graft survival rates in the same groups were 91%, 76%, and 55%, respectively. The major causes of graft loss in cyclosporinetreated patients were nonimmunologic. It is concluded that cyclosporine and prednisone are a safe, efficacious combination for LRD and CAD renal transplantation. The possibility of nephrotoxicity leading to impaired graft function in the early posttransplant period should not preclude the administration of cyclosporine prior to alloantigen presentation.