Chronic rejection has emerged as a major problem in renal transplantation, and clinical trials for prophylaxis and therapy are underway. Use of graft and patient survival as endpoints in prophylactic studies requires long follow-ups to read the endpoint. There is also an obvious need for a starting point for intervention studies. Previously, we formed a histological chronic allograft damage index (CADI), based on numerical scoring of histological alterations compatible with chronic rejection. Using protocol core needle biopsies of 89 functioning grafts 2 years after transplantation and a follow-up of 6 years, we demonstrate now that (a) the CADI at 2 years correlates significantly (r = 0.717, P = 0.0001) with transplant function at 6 years, and (b) that the CADI at 2 years reliably (P = 0.001) predicts the patients who will proceed to clinical chronic rejection later. As protocol core biopsy is an early predictive parameter for chronic rejection, our results suggest that a protocol core biopsy (at 2 years or possibly even earlier) should be included in all clinical investigative protocols dealing with chronic renal allograft rejection.