New methods to accurately measure GFR are needed for both clinical care and research studies involving renal transplant recipients. As new therapies and immunosuppressive strategies become available, a simple and accurate means (such as the MDRD equation) to assess response to therapy will be invaluable. Markers of kidney function (serum creatinine, predicted GFR) are already being used in clinical trials involving renal transplant recipients without appropriate evaluation. The proper validation of equations to predict GFR in transplant recipients must be carried before they can be widely accepted in practice or for use in research protocols. If this study shows that the MDRD equation (or other marker of kidney function) is accurate in transplant patients then we can confidently move forward and use these validated measures of GFR in patient care and future research studies.