Sirolimus has been an important addition to immunosuppressive regimens utilized in kidney transplantation. However, sirolimus can potentiate calcineurin inhibitor (CNI) nephrotoxicity by some still uncertain mechanisms. Studies have demonstrated that withdrawal of a CNI under sirolimus immunosuppression can improve renal function. However, it has yet to be demonstrated that withdrawal of sirolimus from such a regimen can also improve renal function and reverse progressive functional deterioration. We studied 17 patients who developed deterioration of renal function while on a CNI and sirolimus. Once an established deterioration in renal function was noted, sirolimus was withdrawn from the regimen and replaced with mycophenolate mofetil. Out of 17 patients with a negative slope in 1/cr, 15 demonstrated a positive treatment effect (change to a positive slope). On aggregate, renal function improved by 18% (creatinine 2.75-2.24 mg/dL), LDL cholesterol improved, as did hematocrit values after withdrawal. The majority of patients on a CNI and sirolimus regimen who experience deterioration in renal function demonstrate improvement in renal function after withdrawal of sirolimus. This strategy may be particularly useful in those patients where CNI withdrawal is considered to be of high immunologic or metabolic risk.