The stiffness on bending of 7 types of epidural catheters was measured with the help of a cantilever beam. 1415 patients scheduled for lithotripsy, requiring epidural anesthesia, were selected and randomly assigned to receive one of the catheters. The patients were divided into 2 groups according to the resistance to insertion. The incidence of intravenous insertion, subarachnoid location and paresthesia during catheter insertion were assessed. The position of epidural catheters was studied radiographically in 1276 of 1415 patients. There were no significant difference among 7 types of epidural catheters as far as the incidence of intravenous insertion, subarachnoid insertion or straight lying of catheter in epidural space were concerned. When the catheter was hard or pushed against the resistance to insertion, the incidence of paresthesia increased. When the catheter was hard and pushed against the resistance to insertion, transforaminal escape increased. A soft catheter should be chosen to minimize the incidence of paresthesia or transforaminal escape.