In a multicenter trial we investigated the effect of immunosuppressive therapy on graft and patient survival, renal function, and complications in 291 recipients of cadaveric renal transplants. One hundred forty-two patients were randomly assigned to treatment with cyclosporine and prednisone, and 149 to control immunosuppressive therapy (azathioprine and prednisone, with or without antilymphocyte globulin). At three years graft survival was 69 percent in the cyclosporine-treated patients and 58 percent in the controls (P = 0.05). The number of episodes of graft rejection was similar in the two groups, but the severity of rejection was significantly worse among the controls. Patients survival after three years was 90 percent in the cyclosporine group and 82 percent in the control group (P = 0.04). Acute tubular necrosis was an important risk factor for graft loss in both groups. Risk factors for death included diabetes and older age of the recipient. Renal function as indicated by the serum creatinine concentration or creatinine clearance was poorer in the cyclosporine-treated patients than in the controls, but has remained stable in both groups since the sixth month after transplantation. We conclude that, among recipients of cadaveric renal transplants, those treated with cyclosporine, despite having poorer (but stable) renal function, have better graft and patient survival at three years than those treated with alternative forms of immunosuppressive therapy.