Objective To clarify the infection risks and the value of endotoxin determination in urine during extracurporeal shock wave lithotripsy (ESWL). Methocls According to the distribution and complications of upper urinary calculi, 164 patients were divided into five groups. Group A consisted of 48 patients with 1 to 4 renal calculi, which were or lees than 2c,m in diameter. Group B was composed of 24 patients with renal calculus larger than 2cm in diameter or one to multiple renal calculi. Group C was comlposed of 22 patients with. to 3 renal calculi accompanied by 1 to 2 ureteric calculi. Group D consisted of 51 patients with. to 3 ureteric calculi that were 0.5 to 1.2 cm in diameter, respectively. Group E included 19 patients with compricated renal calculus, such as casting and staghom renal calculus. Urine and blood samples of these patients were obtained before and after ESWL, respectively. Their urine samples ware proven sterile prior to treatment. All samples were cultured for bacteria and investigated for endotoxin concentration by the limulus lysate test. Results No significant difference in serum endotoxin was noted before and after ESWL. Blood bacterial cultures ware all negative in all patients after ESWL, similar to those before ESWL. Significant increases in urine endotoxin after ESWL compared with that before ESWL in patients of Groups B, C and E were observed, respectively (P<0.05), There was no significant difference in urine endotoxin after ESWL compared with that before ESWL in patients of Groups A and D. The positive incidences of urine bacterial culturewe significantly increased (P<0.05) in Groups B and C and very significantly increased (P<0.01) in Group E compared with those in Groups A and D. Conc lusions Urinary infection risk following ESWL was lower in patients with one to several renal calculi, which were less than 2 cm in diameter and did not interfere obviously with the urine flow or in patients with 1 to 3 ureterlc calculi that were 0.5 to 1.2 om in diameter. The risk was higher in those with complioeted calculi, such as casting, staghom renal calculus, renal calculus larger than 2 cm in diameter or renal calculi accompanied by ureterlc calculi. For patients with higher infection risk after ESWL, pr ophylactic antibiotics are necessary even if bacteriuria is not present before ESWL. Endotoxin determination in urine is a reliable, sensitive and simple method for the diagnosis of bacterial infection in patients undergoing ESWL.