Laryngoscopy and endotracheal intubation are potent stimuli that can induce increased sympathetic activity, tachycardia and hypertension. The authors studied the effects of intravenous clonidine pretreatment, a centrally acting a2-adrenoceptor agonist, on hemodynamic responses to laryngoscopy and tracheal intubation, and on anesthetic requirements during operation. Forty ASA I -II patients undergoing elective minor general surgery were allocated randomly to receive either 5ug/kg clonidine or 3 ml of 0.9% normal saline as control intravenously 10 minutes before induction of anesthesia. The results obtained were as follows. Compared to baseline values, blood pressure and heart rate at 1 minute after intubation were significantly increased in control group, but significantly decreased in clonidine group. They were maintained at lower values throughout the whole duration of operation in clonidine group than in control group. More doses of fentanyl were needed in the control group but not in the clonidine group during operation, and because of bradycardia and hypotension, atropine or ephedrine was needed in the clonidine group. In conclusion, the elevation of blood pressure and heart rate accompanying tracheal intubation were preventable with less requirement of supplemental fentanyl, but bradycardia and hypotention were infrequently seen as a side effects, when 5ug/kg intravenous injection of clonidine 10 minutes before induction.