Objective To clarify the infection risks and the value of endotoxin determination in urine during extracorporeal shock wave lithotripsy (ESWL).Methods 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 less than 2 crn in diameter. Group B was composed of 24 patients with renal calculus larger than 2 cm in diameter or one to multiple renal calculi. Group C wes composed of 22 patients with 1 to 3 renal calculi accompanied by 1 to 2 ureteric calculi. Group D consisted of 51 patients with 1 to 3 ureteric calculi that were 0.5 to 1.2 cm in diameter, respectively. Group E included 19 patients with complicated renal calculus, such es casting and staghom renal calculus. Urine and blood samples of these patients were obtained before and after ESWL, respectively. Their urine samples were 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 wes noted before and after ESWL. Blood bacterial cultures were 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 culture were 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.Conclusions 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 ureteric calculi that were 0. 5 to 1.2 cm in diameter. The risk was higher in those with complicated calculi, such as casting, staghom renal calculus, renal calculus larger than 2 cm in diameter or renal calculi accompanied by ureteric calculi. For patients with higher infection risk after ESWL, prophylactic 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.