A prospective cohort design will be used. Eligible adult renal transplant recipients at least 3 months post-transplantation will have serum creatinine, albumin, urea, cystatin C, 24-hour urine excretion of urea, 24-hour urine excretion of creatinine, 24-hour urine excretion of protein and GFR measured at study entry and at least 3 months later. GFR will be measured using 99Tc-DTPA. Estimates of the GFR will be made with the MDRD equation and other estimating equations. Renal function will also be assessed by measuring the urinary creatinine clearance and the combined urea and creatinine clearance. The primary analysis will determine the accuracy (proportion of GFR estimates that lie within 30% of measured GFR) of the MDRD equation. Secondary analyses will be performed to determine the bias (mean difference between the measured GFR and estimated GFR) and precision (standard deviation of the difference between the measured and estimated GFR) of the MDRD equation as well as the bias and precision of the change in GFR over twelve months. Similar analyses will be performed for cystatin C and other estimating equations.