Using quantitative sequential camera scintigraphy and simultaneous separated clearance determinations with 131-I-Hippuran and 169-Yb-EDTA renal function was measured applying a new surgical method which permits in-situ kidney perfusion and cooling in animals and patients. While mongrel dogs of 15 kg average weight (control group of N = 5) showed after 1 hour of normothermic ischaemia a postoperative delay of intrarenal transport of 131-I-Hippuran with reduction of 131-I-Hippuran and 169Yb-EDTA clearances, renal function returned to normal on the first postoperative day after 1-hour (N = 5) and 2-hour (N = 5) hypothermic ischaemia. In patients (N = 9) with hypothermic in-situ perfusion of between 40 and 92 min duration a transient postoperative delay of intrarenal 131-I-Hippuran transport and a reduction of the 131I-Hippuran clearance was observed which returned to almost normal 1 1/2 to 3 months after surgery. The results and the significance of the method discussed and are compared with clinical findings and with radiological and laboratory renal function studies.