Renal biopsies were performed when creatinine levels increased > 20% relative to the nadir or when proteinuria was >1 g/day. The nadir level was used as a reference point to obviate the risk of missing the diagnosis of rejection in the low-exposure arm; serum creatinine levels usually fell after the initiation of a low exposure regimen. Biopsies were classified using Banff 1997 criteria by four senior pathologists blinded to the clinical information. CNI-associated nephrotoxicity was graded mild, moderate, or severe according to the Banff 1997 chronicity rejection scores.