As more than 90% of renal grafts retain their function 1 year after renal transplantation, side effects of immunosuppressive therapy gain more and more importance. In a randomised prospective study, we investigated the effects of conversion from cyclosporine A to tacrolimus due to hyperlipidemia in recipients of renal allografts. Fifty-seven patients with stable graft function treated with cyclosporine were randomly assigned to conversion to tacrolimus or continuation of their current therapy and followed for 1 year. Twenty-seven patients were switched and 30 patients remained on cyclosporine A. Cholesterol levels decreased significantly in the tacrolimus group as compared to controls in the intent to treat analysis. When only those patients were evaluated who received cyclosporine or tacrolimus during the whole study, statistical significance was even more pronounced. Triglyceride levels decreased in the tacrolimus group, whereas they increased in controls. Creatinine levels remained stable and no acute rejection was observed. A switch to tacrolimus is a safe alternative in cases of hyperlipidemia after renal transplantation.