The isolated perfused rat kidney (IPK) model was used to assess initial renal function after 24 h preservation in 3 different cold storage solutions: EuroCollins (EC), a solution prepared according to the formulation of Belzer's solution (High-K+ UW) and a high Na(+)-low K+ Belzer UW solution (High-Na+ UW). GFR and FRNa were measured after 24 h cold storage in each of the solutions during 60 min, and were compared to values obtained in a control group in which renal function was measured immediately after the kidneys had been harvested. ATP and CP were measured in fresh renal tissue, in kidneys preserved for 24 h in each solution, in control IPK, and in reperfused IPK after they had been preserved for 24 h. Main results showed that preservation in either solution caused a dramatic decrease in GFR and in FRNa within the first 60 min following reperfusion of cold-stored kidneys. However FRNa was significantly higher in the High-Na+ UW group. ATP and CP content were decreased to approximately 10% of basal values in all experimental groups after cold-storage. Normothermic reperfusion of IPK after cold-storage induced a restoration of ATP levels, but CP content decreased further. There was no significant difference in ATP and CP content between cold-storage solutions, nor any correlation between metabolic and functional parameters.