There is debate concerning the time course and degree of r6coveV possible after relief of complete unilateral ureteric obstruction. This study in dogs investigates these features. One ureter was occluded for varying periods, and then reimplanted into the bladder. Recovery was monitored by Tc-Sn-labelled diethylene triarnine penta acetic acid (D.T.P.A.) scans and renograms together with creatinine clearance studies. The morphological changes were also studied. There was found to be a progressive loss of functional recovery with increasing periods of obstruction, though this was dramatically improved by contralateral nephrectomy once recovery had stabilized. Increased radial scarring developed in the kidney following increasing periods of obstruction.