Background and Purpose: Clonidine is an a2-adrenergic agonist which can be used as an adjuvant in epidural drug mixture and is interesting for its diverse responses, including analgesia and sympatholysis. Many surveys reported contradictory hemodynamic effects of clonidine.We wanted to determine if postoperative epidural clonidine causes hemodynamic instability in patients undergoing lung surgery. We were interested in hypotension and bradycardia and required administration of additional i.v. fluids or drugs during early postoperative period. Materials and Methods: In a prospective randomized double-blinded study we enrolled 24 patients with lung carcinoma scheduled for thoracotomy. They were randomly assigned to morphine group (M) or clonidine group (C). Before operation we inserted an epidural catheter at level T6-7. Group-M received a bolus of 40 μg/kg of morphine in 10 mL saline and group-C additionally to that 4 μg/kg of clonidine. For postoperative analgesia we used a mixture of 4 μg/kg/h of morphine and 10 μg/kg/h of bupivacain in saline for group-M, and additionally to that 0.2 μg/kg/h of clonidine for group-C. Blood pressure, heart rate, amount of fluids and atropine given were monitored during operation and throughout the first 42 hours after operation. Results: The results of this trial demonstrate a marked reduction in systolic, diastolic and mean arterial pressure as well as heart rate throughout the early postoperative study period in group-C. Hypotension demanded treatment with i.v. fluids. Conclusion: High thoracic epidural clonidine used for postoperative analgesia in patients undergoing lung surgery lowers the heart rate and causes hypotension.