To examine the influence of percutaneous nephrolithotomy (PNL) on renal function, we measured the activity of urinary N-acetyl-beta-D-glucosaminidase (NAG) and beta 2-microglobulin (beta 2MG) in patients with nephrolithiasis, before and 3, 5, 7, 14 days and 1 month after PNL. With PNL, renal function was recovered within one month, and PNL was thought to be a more protective method than pyelolithotomy. Recovery of renal function was delayed in the cases in which PNL had been attempted over three times. In the patients with preoperative high-grade hydronephrosis, the excretion of NAG and beta 2MG in the urine was delayed. NAG-index was considered to be a more sensitive parameter than beta 2MG to evaluate renal function. The NAG-index and beta 2MG values of bladder urine were in good correlation with those of nephrostomy urine 5 days or more postoperatively. Measurement of the urinary NAG-index 3, 7, 14, 30 days after PNL operation was considered valuable for determining changes in renal function.