BACKGROUND: Induction of general anesthesia with tracheal intubation and skin incision are potent stimuli that can induce increased sympathetic activity, heart rate and blood pressure. We compared the hemodynamic response and catecholamine concentration during general anesthesia with intravenous clonidine pretreatment, a centrally acting -2 adrenoceptor agonist, and without pretreatment. METHODS: Forty ASA I or II patients aged from 20 to 60 years undergoing elective surgery were randomly allocated to two groups. In group I, 5 ml of 0.9% normal saline as control administered intravenously 10 minutes before induction of anesthesia, and anesthesia was induced with thiopental sodium, succinylcholine and maintained with N2O (2.5L/min)-O2 (2.5L/min)-enflurane (1.3~1.8 vol%). In group II, 4 g/kg clonidine diluted in 5ml of normal saline administered intravenously 10 minutes before induction of anesthesia, and anesthesia was induced with thiopental sodium, succinylcholine and maintained with N2O-O2-enflurane (0.5~1.0vol%) and 2 g/kg/hr clonidine was continuously infused. We measured blood pressure, heart rate and plasma catecholamine at preinduction, 1 minute after intubation (T1), 1 (T2) and 30 minutes after skin incision (T3) and compared with group I. RESULTS: There was statistical significance in systolic and diastolic pressure at T1 between two groups. There was statistical significance in heart rate, epinephrine and norepinephrine at T1, T2 and T3 between two groups. CONCLUSION: The elevation of blood pressure, heart rate and plasma catecholamine accompanying tracheal intubation and skin incision may be prevented by administration of intravenous clonidine.