The concentration of creatinine and urea in plasma and clearances of inulin, endogenous creatinine, urea, and PAH have been measured in pigs on which were performed unilateral nephrectomy (Group A), renal autotransplantation with uretero-vesical anastomosis (Group B), and renal autotransplantation with ureteroureteral anastomosis (Group C). In Groups B and C contralateral nephrectomy was carried out simultaneously. The concentration of creatinine and urea of the pigs in Group A was normal throughout the experimental period. In Groups B and C the concentration rose rapidly immediately after the operation to become normal in the course of 7 days. In Group B a secondary rise was observed between the 7th and 42nd day, in all probability due to ureteral stricture. On the 94th day the clearances of inulin and PAH, calculated per 10 kg body weight, were 17 and 57 ml/min for Group A, 15 and 50 ml/min for Group B, and 18 and 67 ml/min for Group C. The maximal tubular excretion (Tm) of PAH was 19, 19 and 25 mg/min/lO kg body weight for Groups A, B, and C, respectively. These values are 70-100% of the values in normal pigs, indicating that compensatory hypertrophy has occurred in all cases. 67 (57-76) 85 (72-96) 98 (85-108) 113 (99-122) 35 (27-42) 1.9 (0.RBFtOb, increased until 73 days after the trans-Since the experimental animals were killed plantation and then became stabilized.immediately after the last clearance experiment,In Group C clearances as well as RPF,,,, and it was possible to state the clearances both per RBFtotal increased until the 31st day and then 10 kg body weight and per 100 g kidney tissue became stabilized. In calculating the total renal for the final measurements. The average results plasma flow, an extraction percentage of 87 was for Groups A, B and C are shown in Table IV, used, as found by Gyrd-Hansen (9) in normal which also gives the corresponding clearance Pigs. values for normal pigs (9). Acta med. scand. 186