OBJECTIVE : To determine the efficacy of oral clonidine premedication in attenuating the increase of blood pressure and heart rate response to diazepam ketamine induction of anesthesia. DESIGN: Randomized double blind. SETTING : Dr. Cipto Mangunkusumo General Hospital, a national refferal hospital in Jakarta. PATIENTS : Sixty six adult patients (ASA I) presenting elective surgery under general anesthesia. INTERVENTIONS : Randomly selected patients either received 0.3 mg clonidine orally (Group I) or placebo (Group II) as a premedication 60-90 minutes prior to induction. All patients were induced with 10 mg diazepam injected 60 s prior to 100 mg ketamine intravenously. MAIN OUTCOME MEASURE : Blood pressure and heart rate were measured in stimes : prior to premedication, pre induction and 3 times after induction : 1 min, 5 min and 10 min after induction. After this period the study was ended; anethesia continued by attending anesthesiologist. During the study period all of the patients in spontaneously breathing of room air. RESULTS: Blood pressure and heart rate after induction were increased significantly, compared with that before premedication in group II (placebo). In clonidine group (Group 1), comparing to the blood pressure and heart rate before premedication : the heart rate was lower significantly but the blood pressure only significanty lower than before premedication (p < 0.01). CONCLUSION : Clonidine orally 60-90 minutes preoperatively was effective in reducing and even preventing the hypertensive and tachycardia response to induction of diazepam-ketamine.