Canine kidneys have been preserved for twenty-four hours by one of four methods in an attempt to define a suitable technique for application to human cadaveric kidneys before transplantation. Hypothermia was common to all methods, being used alone, supplemented by hyperbaric oxygen or combined with continuous perfusion with 50% blood at 30 mm. Hg pressure in an environment of one or three atmospheres of oxygen. After storage, the kidney was reimplanted into the pelvis of the donor animal and contralateral nephrectomy was performed three weeks later. Consistently successful preservation was achieved by simple hypothermia. Hyperbaric oxygen conferred significant benefit as judged histologically and biochemically. Continuous perfusion was associated with vascular damage and poor subsequent function. In successful experiments long-term survival was obtained irrespective of the storage method used.