Canine kidneys, flushed with either Collins solution or autologous cryoprecipitated plasma, were then stored for 24 hr by either simple cold storage (submersion) in the flushing solution, or by continuous hypothermic pulsatile perfusion with cryoprecipitated plasma. After autotransplantation without contralateral nephrectomy, detailed split renal function studies were carried out immediately as well as 2 and 7 days later. Measurements were made of inulin clearance, maximal transport of p-aminohippurate, reabsorption of sodium, chloride, and glucose, and the reabsorption of free water. Contralateral nephrectomy was performed 7 days after transplantation, following measurement of renal functions on that day, and plasma urea nitrogen and creatinine were measured periodically over the ensuing 3 weeks. Renal function after transplantation was affected very little by the choice of flushing solution, and the course of azotemia that developed following contralateral nephrectomy was the same in all groups. However, the detailed functional measurements showed that during the 7-day period after transplantation, renal function was depressed to a much greater extent in kidneys treated by simple cold storage than in those that had been perfused.