Background:The purpose of this study was to measure the pressure in the anal canal during caudal epidural anesthesia. Methods:The pressure in the anal canal was measured via side-opening perfused catheter in 10 adult patients. The pressure under resting condition was recorded before and following the injection of 10 ml of 1.5% mepivacaine into the caudal epidural space. The pressure when anus was contracted at will was also meassured before and at 5min and 10min after injection. Results: After completion of the injection of mepivacaine, the pressure was gradually decreased. At 4min, the mean resting pressure was significantly decreased to 70% (p< 0.05). The voluntary contractive pressures at 5min and 10min were also significantly decreased to 65% and 51%, respectively (p<0.05). Conclusions:Decrease of pressure in the anal canal appeared surely and early. Pressure in the anal canal can be an effective indicator of the effect of caudal epidural anesthesia.