Eleven patients with recent kidney transplants have undergone serial pelvic imaging after autologous platelet labelling with indium-111. Rejection was accompanied by marked platelet deposition in the graft, whereas acute tubular necrosis was characterized by minimal platelet accumulation. The method has been quantified by comparing counts over the graft to counts from a similar area on the opposite site, and appears to distinguish between the two main causes of renal failure after transplantation. In addition, complications of transplant surgery may be demonstrated.