In order to investigate the effect of electromagnetic shock waves on proximal tubular renal function, we measured the urine levels of the lysosomal enzyme N-acetyl-beta-glucosaminidase (NAG) prior to, 1 hour, 1 day, and 1 week after extracorporeal electromagnetic lithotripsy (ESWL) in 50 patients with urinary stone disease. Mean NAG level which was 5.18+0.09 U/l prior to ESWL increased to 5.29+0.09 U/l in the first hour and to 10.7+0.19 U/l on the first day after ESWL (p<0.001). The level returned to pre-ESWL values one week after ESWL (5.27+0.09 U/l). These findings show that extracorporeal electromagnetic shock waves cause significant damage to the proximal tubular epithelium of the kidney; however, these changes return to normal in the first week. © 1994 Akadémiai Kiadó.