In experiments on dogs we observed that the remaining of the peripelvic and periureteral tissue in taking from the kidney is not decisive for the blood supply of the ureter. That these findings are important also for the clinic is confirmed by the following fact: in order to draw the ureter through the natireflux tunnel, 2-4 cm of the periureteral tissue must be removed. However, we never observed a necrosis restricted to this place. 2. In all experiments the blood supply of the upper half of the donor ureters was confirmed without any mistake. Therefore we recommend to shorten the ureter to this length for the UNC. 3. The preservation by means of hypothermy or permanent machine perfusion has no negative effect on the blood supply of the ureter.