BACKGROUND: Esmolol has been recommended to prevent tachycardia and hypertension induced by tracheal intubation in several studies, but these studies are based on mean values of changes of vital signs. Therefore, the recommended doses are not guaranteed to be precise effective dose. METHODS: According to esmolol dose, 140 patients were randomly alldegrees Cated to 7 groups of 20 patients. After intravenous thiopental and vecuronium followed by mask ventilation of 3 minutes with enflurane, nitrous oxide and oxygen, one of the dosages of esmolol 0, 0.2, 0.3, 0.45, 0.5, 0.6, 0.8 or 1.0 mg/kg was administered. Ninty seconds later, tracheal intubation by direct laryngoscopy was performed. After then heart rate was monitored continuously and blood pressure was measured 5 times at intervals of 1 minute. The highest heart rate and systolic blood pressure were recorded. If the highest heart rate was beyond 100/min or highest systolic blood pressure was beyond 170 mmHg, we regarded this cases as 'unprotected' case. By logistic regression, we calculated the doses of esmolol which reduce the incidence of tachycardia, systolic hypertension and unprotection below 5% respectively. RESULTS: The appropriate doses of esmolol for prevention of tachycardia, systolic hypertension and 'unprotection' were 0.95 mg (95% CI: 0.77~1.33 mg), 0.38 mg (95% CI: 0.21~1.05 mg) and 0.93 mg (95% CI: 0.78~1.23 mg) respectively. CONCLUSIONS: In anesthetic induction and tracheal intubation with thiopental and vecuronium, esmolol 0.78~1.23 mg/kg was appropriate for preventiion of tachycardia ( > 100 bpm) and systolic hypertension ( > 170 mmHg).