A new renal perfusate of modified intracellular electrolyte composition made hyperosmolar with mannitol and requiring no additional additives was successfully used to preserve canine kidneys “ex-vivo” for 48 hours by initial perfusion and hypothermic storage. The new perfusate was also successful in protecting totally ischemic canine kidneys from the lethal effect of two-hours of normothermic exposure “in-vivo”. — The preservation technique is uncomplicated, the materials involved are inexpensive, and the preservation apparatus is readily transportable.