Extracorporeal shock wave lithotripsy has become the treatment of choice for upper urinary tract stones. We evaluated the impact of a new lithotripter on the kidneys of 14 nonobstructed patients treated for renal stones, using several physiological parameters and renal ultrasonography. Glomerular filtration rates (GFR) were estimated from the renal scan. Complete disintegration of the stone was accomplished in all but one patient. Treatment did not alter the serum parameters or the renal ultrasonography. Also, no changes were found in the GFR on the follow-up renal scans in both kidneys. The implications of these findings are discussed.