BACKGROUND: Vasoconstrictors have been used as an adjunct to local anesthetics to prolong the duration of spinal anesthesia. Recently, clonidine, an 2-receptor agonist has been shown to prolong the duration of spinal anesthesia following intrathecal administration. Bupivacaine has been used for spinal anesthesia and compared with tetracaine in recent studies. We have undertaken this study to further evaluate the effect of clonidine in hyperbaric 0.5% bupivacaine spinal anesthesia. METHODS: Thirty patients who were scheduled for lower limb or urologic operation were divided into 2 groups: Group A (hyperbaric bupivacaine 13 mg, 2.6 ml + N/S 1 ml), Group B (hyperbaric bupivacaine 13 mg, 2.6 ml + clonidine 150 g, 1 ml). We used standardized techniques and injected above drugs to group A and B intrathecally for spinal anesthesia. We investigated the onset and the duration of spinal anesthesia along with hemodynamic changes (blood pressure and heart rate) in patients. RESULTS: There were no significant differences in the onset of spinal anesthesia and hemodynamic changes between two groups. The time taken to recover from the nerve block was more prolonged in the group B (touch 225, pain 262, foot dorsiflexion 271, knee flexion 290 minutes) than group A (touch 154, pain 188, foot dorsiflexion 198, knee flexion 216 minutes). There were no significant differences in sedation, and in experiencing dry mouth and other side effects between two groups. CONCLUSION: Intrathecal clonidine 150 g has been proved to prolong the duration of hyperbaric 0.5% bupivacaine spinal anesthesia without neurotoxicity or dangerous hemodynamic depression. Therefore, clonidine can be used as an effective adjunct in hyperbaric bupivacaine spinal anesthesia.