BACKGROUND: Tracheal intubation by direct laryngoscopy induces frequently transient hypertension, tachycardia and arrhythmia. The purpose of this study was to examine the effect of esmolol and clonidine in attenuating the changes of blood pressure and heart rate by tracheal intubation. METHODS: Eighty patients were randomly divided into four groups: Group 1 (control , n=20), Group 2 (esmolol 0.5 mg/kg IV, n=20), Group 3 (clonidine 4 mcg/kg PO, n=20) and Group 4 (clonidine 4 mcg/kg PO and esmolol 0.5 mg/kg IV, n=20). The clonidine premedication were given orally with a sip of water 90 minutes before induction of anesthesia. Anesthesia was induced with thiopental 5 mg/kg, vecuronium 0.1 mg/kg, 50% nitrous oxide in oxygen and 2 vol % enflurane. After 5 minutes, tracheal intubation was performed. Patients in the group 2 and group 4 were given esmolol 0.5 mg/kg 90 seconds prior to tracheal intubation. Blood pressure and heart rate were measured at ward, preinduction, preintubation, immediately after intubation, 1, 3 and 5 minutes after intubation. RESULTS: After tracheal intubation, the increase in systolic blood pressure was supressed significantly in the clonidine-treated patients (Group 3, Group 4) compared with control group (p<0.05). The attenuating effect on increase of mean arterial pressure(MAP) was sustained longer in group 4 than group 3. Heart rate increased after tracheal intubation in all groups, but were markedly increased in the control group (p<0.05). The differences of MAP which measured at preinduction and immediately postintubation were smaller in group 4 than control group (p<0.05). The differences of heart rate which measured at preinduction and immediately postintubation were smaller in group 4 than group 1 or group 3 (p<0.05). CONCLUSIONS: Esmolol 0.5 mg/kg given as bolus, is effective for controlling the increase of heart rate but not in attenuating increase of blood pressure. Oral clonidine is effective for controlling the increase of blood pressure but not in attenuating increase of heart rate. Therefore esmolol combined with oral clonidine results in effective control of both heart rate and blood pressure.