Phosphocreatine (PCr) is a critical intracellular energy reservoir used in the regeneration of ATP. The aim of this study was to determine the efficacy of exogenously added PCr on preservation of renal function in an in vitro model. The renal artery and ureter of a rat were cannulated and the kidney was subjected to 45 min of normothermic in vivo ischemia. The kidneys were then perfused ex vivo with either a Krebs-bicarbonate solution (Krebs) or a Krebs solution containing 3 mM PCr or an osmotically balanced solution containing 3 mM PCr. Our results indicate that the perfusion of kidneys subjected to 45 min of warm ischemia with solutions containing PCr resulted in significant improvements in GFR, RPF, and V, FRNa and FRH2O compared to KREBS alone. This suggests that the important factor in preservation of kidney function after an initial ischemic insult may be the addition of PCr rather that the electrolyte solution used.