BACKGROUND: Tracheal intubation can cause sympathetic stimulation such as hypertension and tachycardia. Many drug are used for reducing the incidence of hypertension and tachycardia induced by intubation. Among these drugs, fentanyl can be used with good result. The purpose of this study was to find the appropriate fentanyl injection time before intubation when a small dose (3 microgram/kg) was used. METHODS: We studied 82 ASA class 1 2 patients, scheduled for gynecological elective surgery, randomized into 5 groups. Group 1 received no fentanyl before intubation, and groups 2, 3, 4 and 5 received 3 microgram/kg fentanyl at 7 min, 5 min, 3 min and 1 min before intubation, respectively. The blood pressure and heart rate were checked at preinduction and post-intubation periods for 5 minutes. RESULTS: The increase of the heart rate was significantly lower in groups 2 and 3 than in group 5 just after intubation. Furthermore the increase of the mean blood pressure was significantly lower in groups 2, 3 and 4 than in group 5 just after intubation. The incidence of tachycardia and hypertension was significantly lower in groups 2, 3 and 4 than in group 5 just after intubation. CONCLUSIONS: When a small dose of fentanyl was used to blunt the intubation induced sympathetic stimulation, the appropriate time was prior to 3 minutes before intubation.