Three kidneys preserved as though for transplantation became available for study. The clinical details relating to the donors and methods of preservation by simple hypothermia and pulsatile perfusion are presented. Light microscopic and ultrastructural features observed following perfusion fixation of the kidneys are described. All three kidneys showed some reversible ischemic cell damage, but only one showed evidence of ischemic cell damage that was considered to be irreversible. The latter was seen focally in the pars recta of the proximal convoluted tubules and in the ascending thick limb of the loop of Henle. The irreversible changes were present in the kidney that had undergone the longest period of simple hypothermic storage prior to transfer to pulsatile perfusion preservation. The similarity of the findings to those seen in vivo in the rat after one hour of total renal ischemia, followed by 24 hours' reflow, is discussed; a hypothesis is suggested to explain the site of the irreversible injury seen in the kidneys under study.