Intrathecal clonidine injection induces analgesia without significant respiratory depression, but decreases blood pressure and causes sedation. Injection of spinal cholinesterase inhibitor alone increases blood pressure in animals, and enhances clonidine induced analgesia. To evaluate the effect of pretreated pyridostigmine on the change of blood pressure and heart rate, clonidine was injected intrathecally in cats. We divided fifteen cats into three groups and administered saline(0.5 cc) to group 1, pyridostigmine(0.5 cc, 2.5 mg) to group 2, pyridostigmine(0.5 cc, 2.5 mg) and glycopyrrolate(0.5 cc, 0.1 mg) to group 3 before 20 minute of clonidine injection and measured mean arterial pressure, heart rate, P CO2 and central venous pressure. The results were as follows: 1)After clonidine injection, all mean arterial pressure values were significantly reduced in group 1, but in group 3, 20, 30 and 40 minutes values were significantly reduced, and 10, 40 minutes values after clonidine injection were not reduced significantly in group 2 compared to group 1. 2)After clonidine injection, heart rates were significantly reduced in all groups, but there was no significant difference between group 1, group 2 and group 3. 3)There was no significant difference of central venous pressure in any groups. 4)There was no significant difference for reversal of pyridostigmines effect by glycopyrrolate. Based on these results, these data suggest that pyridostigmine pretreatment counteracts clonidine induced hypotension, but further study of spinal az adrenergic-cholinergic combination for pain therapy is needed before clinical application.