Using a retrospective analysis we compared 79 recipients of cadaveric renal allografts who were treated with cyclosporine as the sole initial immunosuppressant and 29 concurrent transplant recipients treated with conventional immunosuppressants. The cyclosporine-treated group had a slightly higher actuarial patient survival at four years (86 per cent vs. 76 per cent). Actuarial graft survival at four years was 70 per cent in the cyclosporine group, as compared with 62 per cent in the conventionally immunosuppressed group. The incidence of acute rejection episodes was 62.1 per cent in the former and 65.5 per cent in the latter. Nephrotoxicity was managed either by reduction of the dose of cyclosporine or by conversion to conventional immunosuppression. Monitoring of trough serum levels of cyclosporine facilitated its administration. Serum creatinine levels have been higher in cyclosporine-treated patients with functioning grafts, but graft deterioration has not occurred after more than three years. Cyclosporine provides adequate immunosuppression for patients with renal allografts. At four years, the rates of patient and graft survival remain superior to those with conventional immunosuppression. In 41 per cent of patients the use of steroids was completely avoided. The longer-term results of this powerful immunosuppressive agent are not yet known. (N Engl J Med 1984; 310: 148–54.)