BACKGROUND: Sympathetic blocking agent, esmolol (selective beta 1 blocker) or labetalol ( alpha and beta blocker) would prevent the hypertension and tachycardia from endotracheal intubation. We have carried out the study to see the effects of esmolol or labetalol on the blood pressure, heart rate, rate pressure product and plasma catecolamines during the endotracheal intubation. METHODS: Thirty-three ASA physical status 1 or 2 adult patients were allocated into three groups; Group I:control (n=10), Group II:esmolol (n=11) and Group III: labetalol (n=12). In Group I, 2 ml of normal saline, in Group II, 1 mg/kg of esmolol, and in Group III, 0.2 mg/kg of labetalol were given 3, 2 and 4 minutes before endotracheal intubation. Blood pressure and heart rate were measured after arrival at the operating room, before endotracheal intubation and after endotracheal intubation at 15, 60, 120, 180 and 300 seconds interval under the inhalation anesthesia (enflurane-N2O-O2). Rate-pressure product was calculated from the heart rate and systolic blood pressure (RPP = heart rate x systolic blood pressure). The plasma cathecolamines, dopamine, norepinephrine and epinephrine, were measured before intubation as a baseline value and 2 minute after intubation. RESULTS: Systolic blood pressure, rate-pressure product and heart rate were significantly lower in esmolol and labetalol groups than in control group after intubation ( p<0.05). Esmolol reduced the heart rate and the rate-pressure product than labetalol, but statistically there were no significance (P > 0.05). Plasma level of dopamine, norepinephrine and epinephrine showed higher values after intubation in all three groups ( p<0.05). But there were no difference among groups (P>0.05). The side effects of esmolol and labetalol did not appear at all. CONCLUSION: 1 mg/kg of esmolol given 2 min before intubation or 0.2 mg/kg of labetalol given 4 min before intubation reduce increasing of blood pressure and heart rate, caused by adnergic response following endotracheal intubation, significantly. The reason is that esmolol and labetalol do not decrease release of catecholamines but attenuate responses of elevated catecholamines following endotracheal intubation.