Background: Clonidine, a α₂-receptor agonist, has sedative and decrease the MAC of anesthetics. Clonidine also has analgesic properties following intrathecal administration. This study evaluates the effects of clonidine on the onset time and duration of analgesia when added to bupivacaine for brachial plexus block. Methods: Forty patients of ASA physical ststus I and II who scheduled for elective upper limb surgery were divided into two groups in randomized, double-bline fashion. The brachial plexus block was performed with 30 ml of 0.33% bupivacaine plus saline(1 ml; n=20)or clonidine(150 ug, 1 ml; n=20). The following variables were recorded; onset time, duration of analgesia, sedation, heart rate and blood pressure. Results: The onset time produced with the addition of clonidine was faster(15.6±5 vs 19±4 min). The duration of block, heart rate and blood pressure were not different between the groups. There were more sedation in the clonidine group. Conclusions: From the above results, adding clonidine to bupivacaine is an attractive adjuvants for brachial plexus block. (Korean J Anesthesiol 1996; 30: 610-614)