Previous studies have shown that adenosine triphosphate-magnesium chloride (ATP-MgCl2) administered after 30 to 60 min of renal ischemia ameliorated the resulting acute renal failure in different species of animals. The purpose of this study was to determine whether addition of ATP-MgCl2 to the perfusate during renal preservation, prior to transplantation, might improve renal function. Dog kidneys were subjected to normothermic ischemia for 35 min, after which they were preserved by pulsatile perfusion for 24 hr at 7 C. The perfusate contained albumin in a balanced electrolyte solution with and without ATP-MgCl2. Following 24 hr of pulsatile perfusion, the kidneys were autotransplanted and renal function was determined 3 days post-transplantation. The results indicated that dog kidneys subjected to ischemia followed by perfusion preservation developed severe oliguric renal failure 3 days after transplantation. However, if ATP-MgCl2 was added to the perfusate, such kidneys demonstrated markedly improved renal function and ATP levels. These results indicate that kidneys which have been subjected to episodes of warm ischemia could be salvaged by addition of ATP-MgCl2 to the perfusate. © 1981 by The Williams & Wilkins Co.