We examined whether prophylactic antibiotics are necessary or not during the ESWL treatment for patients with urolithiasis. Twenty-eight patients with unilateral renal or ureteral stones composed of calcium oxalate, calcium phosphate or the mixed stones were treated with MPL 9000 between May 12 and September 30, 1992. Although 17 patients (60.7%) had complications of pyuria before treatment, none of the 28 patients had taken any prophylactic antibiotics during the treatment. To evaluate the clinical signs of infection, we examined the white blood cell count, in blood and urine sediment and serum C-reactive protein (CRP) value at the time of 1, 3 and 7 days after ESWL treatment, and body temperature and urine culture at the time immediately after the treatment in addition to the above-mentioned days, compared with the pre-treatment data. White blood cell count at one day after ESWL treatment was significantly elevated both in the patients with and without pyuria, while body temperature at the time immediately after the treatment was significantly elevated only in the patients with pyuria. Six of the 23 patients (26.1%) with preoperative sterile urine and who had urine culture immediately after ESWL, had bacteriuria. However, none of the 28 patients had any clinically significant infectious complications during ESWL treatment without any antibiotics therapy. We concluded that it is important to examine urine culture immediately after ESWL treatment for early protection from complication of urinary tract infection and that administration of prophylactic antibiotics is not necessary during ESWL treatment for patients with non-infection stones even concomitantly with pyuria.