Radionephrographies were performed in 23 hypertensive patients before and after 28 transluminal dilatations (PTD) of their stenosed renal arteries. The changing clearances for both kidneys (global = Cl<sub>gl</sub>) and for stenosed and contralateral kidneys (Cl<sub>st</sub> and Cl<sub>co</sub>) were followed for three groups, dependent on their clinical outcome, as well as the parenchymal transit time (re-entry time) for the diseased (Rt<sub>st</sub>) and contralateral kidneys (Rt<sub>co</sub>): (A) Normalized hypertension: for 9 patients the preoperative Cl<sub>co</sub> was never lower than 150 ml/min, but increased significantly after PTD. Rt<sub>st</sub> fell significantly, Rt<sub>co</sub> remained constant. Mean increase in Cl<sub>gl</sub> = 91 ml/min (+25%). (B) Improved hypertension: in 12 patients Cl<sub>st</sub> and Cl<sub>co</sub> had been lower than with those in group A; postoperatively Cl<sub>st</sub> increased, Rt<sub>st </sub>fell significantly. The Rt<sub>co</sub> was prolonged early after PTD but normalized later. (C) Permanent hypertension: for 7 of these patients there were no preoperative criteria for a discrimination against the other groups. But in all Rt<sub>st</sub> did not normalize, and Rt<sub>co</sub> increased early after PTD. Even in later examinations Rt<sub>co</sub> remained higher than preoperatively. These results imply that the success of PTD depends mainly on the behavior of the contralateral kidney. The examination 1 day after the PTD gives an optimal prognosis concerning the end result.