When we perform the regional blockade, we usually addit epinephrine to the local anesthetics for the purpose of lengthening anesthesia time and preventing the systemic reaction of local anesthetics. In that situation, epinephrine produces decrease in serum potassium concentration and changes in electrocardiogram. We investigated the influence of propranolol on changes in serum potassium and ECG induced by brachial plexus block with 30ml of mixture of local anesthetic (2% lidocaine +0.5% bupivacaine) which contains 1:200,000 epinephrine. The subjects classified as following two groups: Group l : Brachial plexus block with mixture of local anesthetic and 1:200,000 epinephrine(n=20). Group ll : Pretreated with 2 mg of propranolol(slow intravenous injection for 5 min. before block) and performed as Group l. The results were as follows: 1) Group l showed statistically significant decrease of serum potassium after 10, 20, 30 min. of block(p<0.05). Group ll did not show any significant change. 2) Group l showed progressive flattening of T wave and appearance of U wave (25% of pts) in ECG as the serum-potassium decreased progressively, but Group ll did not sho any significant change. 3) The epinephrine mediated beta-adrenergic stimulation may be considered as the cause of epinephrine induced hypokalemia during brachial plexus block.