Obstruction on the urinary tract eventually results in damage to the kidneys and loss of function. The questions that concern the clinician are the degree of nephron loss in that kidney and the potential for recovery following the relief of obstruction. 99mTc DMSA accumulates in tubule cells and has been proposed as a marker of the tubular mass. The authors estimated the renal uptake ratio of 99mTc DMSA for the degree of nephron loss corresponding to duration of hydronephrosis following left ureteral ligation in 5 NewZealand white rabbits and the potential for recovery following percutaneous nephrostomy of hydronephrosis in 24 rabbits. While the renal uptake ratio of 99mTc DMSA of the kidney with unilateral hydronephrosis following ureteral ligation reduced dramatically within 24 hour, that of the opposite healthy kidney increased, and the total renal uptake ratio was same as normal functioning kidneys before ureteral ligation. Upon ureteral release, there was no evidence of definite recovery or impairment in the experimental kidneys for 5 days. The authors conclude that a combination of ureteral release and administration of some drugs such as renal vasodilator or diuretics is an appropriate treatment for the recovery of function in unilateral hydronephrosis.