In 60 patients with hypertension and unilateral renal artery stenosis (URAS) radio-hippuran renograms were performed before and 6 weeks after anatomically adequate percutaneous transluminal angioplasty (PTA). Two characteristics of the renographic curves have been analyzed: the difference in time to peak (DTP) between the affected and contralateral kidneys, which would be expected to be positive in blood flow impairment, and the relative hippuran uptake (RHU) in the second minute by the affected kidney as compared with the total uptake by both kidneys: this would be less than 50% in the case of stenosis. Before PTA, both variables were predominantly abnormal. The DTP did not predict the blood pressure response to PTA. The group of patients with a RHU between 25 and 45% comprised all cured patients and predicted a more favorable response of the blood pressure than a RHU of less than 25% and especially more than 45% which group contained 83% patients whose blood pressure failed to respond after PTA. After PTA the DTP did normalize in the majority of patients, but this was not related to the blood pressure response. The RHU increased in patients in whom it had been low initially, but frequently remained low ( < 45%). The increase of the RHU was significantly higher in patients with a favorable blood pressure response. Pretreatment with captopril did intensify the abnormal curves of hippuran and of DTPA renograms in 6 patients with URAS who did respond favorably to PTA. There was no such deterioration in 2 patients whose blood pressure did not change sufficiently after PTA or in 4 patients without renal artery stenosis. In conclusion, renography can to some extent predict the effect of PTA on the blood pressure; possibly captopril pretreatment can improve its predictive ability. Sequential renographies can be used as an indication of improvement of the renal function after PTA.