The efficiency of hypothermic mechanical perfusion and hypothermic storage, resp., for kidney preservation was to be examined. For this purpose dog kidneys were subdued to 0 to 60 min of warm ischemia, then preserved for 12--72 hours and thereafter transplanted. It could be concluded: 1. Hypothermic mechanical perfusion makes a successful 72 hour preservation possible with excellent kidney function immediately after transplantation. After 30 minutes of warm ischemia the preservation period should be limited to 24 hours. 2. Hypothermic storage is inferior to mechanical perfusion concerning the immediate function after transplantation: 24 hours storage time and 15 minutes of warm ischemia should not be exceeded. 3. Kidney function decreases exponentially by the time of preservation. This means that the warm ischemic period and the preservation time, resp., should be as short as possible to get an undamaged kidney after transplantation: the shorter the preservation period the better the kidney function after transplantation.