This study showed that assessment of the complement-binding capacity of donor-specific anti-HLA antibodies may help identify patients at high risk for kidney-allograft loss and may improve risk stratification to guide treatment. Despite considerable advances in transplantation, the induced alloimmune response remains a major determinant of late kidney-allograft loss. 1 – 3 In the United States and Europe, thousands of kidney transplants fail each year, and kidney-allograft failure is a major cause of end-stage renal disease, leading to increased morbidity, mortality, and costs. 4 , 5 One of the most important advances in transplantation medicine has been the recognition that anti-HLA antibodies are destructive. 6 – 10 Various studies over the past decade have indicated that the alloimmune response, mediated by anti-HLA antibodies, plays a key role in the failure of kidney allografts; this concept has been extended . . .