There is no simple analytical test. Radionuclide diuretic renography (RDR), being a dynamic imaging study reflecting the function of the kidney and the urodynamics of the urinary tracts, has the potential to predict the outcome of surgery in obstructive uropathy. In 12 sheep, we occluded one ureter for a maximum of seven weeks and followed up for a maxim of five weeks after release of occlusion. Repeated Tc-99m DTPA diuretic renography studies were performed and the results were correlated with the duration of complete ureteric occlusion. The renal uptake percentage and the extraction slope of the time activity curve (TAC) showed progressive and steady decrease over the period of the occlusion. By the fifth week there was very low uptake (less than 18%) and the TAC was almost flat, suggestive of severe nephropathy. The parenchymal transit time index (PTTI) showed immediate rise after occlusion but with no progressive increase in its value. By the fifth week it dropped down to normal. After release, the recovery of function showed good correlation with the renal uptake percentage and extraction slope of TAC before release of occlusion. Therefore both these parameters, rather than PTTI, can be used to predict the outcome of surgery before the release of complete obstruction of the ureter.