BACKGROUND: Tracheal intubation is accompanied by varing degrees of sympathetic stimulation as reflected by increases in the heart rate and blood pressure. Several trials with pharmacologic agents have been conducted to reduce changes in blood pressure and heart rate. The aim of this study was to determine the appropriate dose of remifentanil required to prevent hemodynamic changes immediately after tracheal intubation in patients anesthetized with sevoflurane-N2O-O2. METHODS: Ninety ASA class I or II patients scheduled for elective surgery were divided randomly into 6 groups: I, II, III, IV, V, and VI. After induction of anesthesia with thiopental, vecuronium, and sevoflurane 2 vol% with N2O/O2 50/50 via a face mask, saline, 0.3, 0.4, 0.5, 0.6, and 0.7microgram/kg of remifentanil were given to group I, II, III, IV, V, and VI, respectively. Tracheal intubation was carried out for 90 seconds after drug administration, for patients in each group. The heart rate (HR), mean arterial pressure (MAP), and end tidal sevoflurane concentration (ETSEVO) were measured at preanesthesia, before intubation, and at 1 min after intubation, for each patient. RESULTS: HR and MAP at 1 min after intubation were increased in groups I and II, and were unchanged in groups III, IV, V and decreased in group VI, as compared to preanesthetic values. CONCLUSIONS: A single injection of 0.4, 0.5, 0.6microgram/kg of remifentanil was an appropriate dosage to prevent hemodynamic changes after tracheal intubation without adverse effects in patients anesthetized with sevoflurane-N2O-O2.