The light and electron microscopic morphology of 57 cadaver renal allografts was assessed at the time of procurement and again after revascularization. Twenty-two kidneys (39%) did not function immediately after transplantation and 19 of these (86%) contained morphologic evidence of acute tubular necrosis (ATN) in the procurement biopsy. The morphology of the post-transplant biopsy was abnormal in all 22 kidneys with delayed function. There was a wide spectrum of morphologic change between the time of procurement and revascularization in all kidneys with normal function. These changes were mild in nature, were usually confined to proximal tubules, and were of unknown clinical significance. The morphology of kidneys that were damaged by the time of procurement was surprisingly different after storage with simple hypothermia (ice) than after storage with hypothermic pulsatile perfusion. The changes attributed to ice storage included endothelial swelling and vacuolation with obliteration and collapse of capillary lumens, fracture and splitting of peritubular basement membrane, and hyalinization of the renal interstitium. It was unknown whether these morphologic abnormalities were associated with delayed recovery of function of the injured kidneys.