BACKGROUNDS: In man, adding clonidine to local anesthetics results in an increased duration of spinal, epidural and peripheral nerve blocks such as femoral nerve block. The purpose of this study was to compare the effects of intramuscular or adding clonidine to mepivacaine on the duration of analgesia after brachial plexus block. METHODS: After informed consent, 30 ASA 1 or 2 adults patients scheduled for elective upper limb surgery under brachial plexus anesthesia were included in this study. Brachial plexus block with Supraclavicular approach was performed following paresthesia. 40ml of 1.5% mepivacaine was injected in the brachial plexus sheath in all patients. In group 2, 150 ug of clonidine IM, 30 min before the procedure. In group 3, 150 ug of clonidine added to mepivacaine in brachial plexus sheath. Onset of anestheasia and duration of anesthesia and analgesia were assessed. Blood pressure and sedation score was monitored. Statistical analysis was done with ANOVA. RESULTS: Duration of anesthesia were significantly increased in group 3 (217.0 +/- 56.2 min by pinprick) compared to group 1 (176.0 +/-26.3 min). Duration of analgesia were significantly increased (p<0.05) in group 3. (229.0 +/- 43.3 min) compared to group 1 (186.0 +/- 20.0 min). Blood pressure was not significantly different in the three groups. A sedation was observed in group 3, especially from 20 min to 180 min after injection of drug. CONCLUSION: 150 ug of clonidine added to mepivacaine for brachial plexus block increases duration of anesthesia and analgesia without any significant side effects.