We investigated 117 patients undergoing percutaneous nephrolithotomy, percutaneous nephrostomy, ureterorenoscopy, the push-back or push-bang procedure for ureteral stones, Double-J* ureteral stenting plus extracorporeal shock wave lithotripsy (ESWL), ESWL alone or cystoscopy. Blood samples obtained before, during and 1 hour after the procedure were cultured and assayed for endotoxin and tumor necrosis factor. Also, culture was done of the urine preoperatively and postoperatively, and the stones when they could be retrieved. There was a temporal relationship among bacteremia, endotoxemia and elevation of tumor necrosis factor. An unexpected finding was peroperative endotoxemia in a significant number of patients with stones. Risk factors noted for postoperative bacteremia, endotoxemia and/or elevation of tumor necrosis factor included preoperative endotoxin level, type of procedure, presence of preoperative bacteriuria and pyuria. With respect to the procedure the risk was greatest after the push-back method and least after cystoscopy (push-back method greater than percutaneous nephrolithotomy/percutaneous nephrostomy greater than Double-J stenting plus ESWL greater than ureterorenoscopy greater than ESWL greater than cystoscopy). If the risk factors are measured preoperatively it may be possible to identify the risk of postoperative bacteremia/endotoxemia and, therefore, septic shock postoperatively. Our patients appear to be a good clinical model to investigate the problems related to septicemia.