The general use of bilateral rather than separate renal function evaluation has led to the publication of conflicting results concerning the effect of percutaneous transluminal renal angioplasty (PTRA) on renal function, especially in patients with atherosclerotic renal artery stenosis. The aim of this study was to evaluate prospectively, in standardized conditions, split renal function (SRF) and GFR outcome after successful PTRA, by measuring single kidney GFR with synchronous inulin or (51)Cr-ethylenediaminetetraacetic acid clearance and (99m)Tc-diethylenetriamine pentaacetic acid scintigraphy, in a well-defined population of patients with unilateral renal artery stenosis. Thirty-two consecutive hypertensive patients (18 with atherosclerotic and 14 with dysplastic disease) with significant unilateral stenosis of the main native renal artery (> or = 60%) and normal renal function were included in the study. Renal and angiographic follow-up evaluations were performed 6 mo after PTRA. PTRA alone or combined with stenting (n = 2) was technically successful in all patients. Repeat PTRA was necessary in two patients, evaluated 6 mo after the second PTRA. Six mo after PTRA, total GFR had increased slightly but significantly in the 29 patients with positive lateralization indices. SRF and single-kidney GFR of the stenotic kidney increased significantly, whereas concurrently the GFR and SRF of the nonstenotic kidney decreased significantly. Six mo after successful PTRA reducing renal ischemia, a reversal of both the hypoperfusion of the stenotic side and the hyperperfusion of the nonstenotic side was observed, which was accompanied by a slight increase in total GFR.