Our previous studies indicate that the blockade of the sympathetic nervous system by spinal anesthesia or epidural anesthesia inhibits the release of TXA2 induced by limb ischemia with thigh tourniquet in patients with lower limb surgery. The present study was undertaken to confirm this phenomenon in anesthetized dogs. Twenty one anesthetized dogs underwent 60 min occlusion of the abdominal aorta and the inferior vena cava, followed by reperfusion. They were randomized into three groups: no treatment group and pretreatment groups with either 2 ml of 0.5% bupivacaine intrathecally or 4 mg.kg-1 of labetalol intravenously. In no treatment group plasma TXB2 levels were increased significantly after reperfusion. However, prior treatments with bupivacaine intrathecally or labetalol intravenously inhibited the increases in plasma TXB2 levels after reperfusion. These results suggest that limb ischemia stimulates the TXA2 production, which may be influenced not only by endothelial cell damage and the generation of oxygen free radicals but also by the activation of the sympathetic nervous system.