Clonidine, an 2 agonist, has been shown to be effective as preanesthetic medication in adults. To evaluate the effects of clonidine on the sedation and cardiovascular changes induced by intubation, we administered clonidine (2.0-2.5g/kg, 4.5-5.0g/kg, peros) 90-120min before induction of anesthesia. We measured heart rate, systolic pressure and diastolic pressure before premedication, before induction, after intubation and 5, 10, 15, 20 and 30 min after intubation and evaiuated sedative sction before induction. The results are as follows: 1) Before intubation heart rate decreased significantly in both clonidine groups compared with diazepam group (P<0.05). 2) Before intubation clonidine 4.5-5.0g/kg group produced a significant reduction in systolic pressure compared with diazepam group (P<0.05). 3) After intubation systolic and diastolic blood pressure increased in all group but the increasing rate was significently less then in clonidine 4.5-5.0g/kg group (P<0.05). 4) After intubstion the increase in heart rate in both clonidine groups were significsntly less than in diazepam group (P<0.005). 5) Sedative actions were not significantly different in all groups.