Thiopental sodium, a water-soluble barbiturate derivative with pH 10.0, reaches brain tissue in its highest concentration in about 50 seconds after intravenous injection. Blood concentration then decreases according to redistribution. Patients who are given midazolam as an induction agent are known to awake from general anesthesia relatively more slowly than those given pentothal sodium. Fentanyl, a potent analgesic, has been used in balanced anesthesia because of its minimal cardiovascular effects. In the present study, the effects of pentothal sodium, midazolam and midazolam-fentanyl on cardiovascular changes to endotracheal intubation during anesthetic induction were compared. Sixty patients of ASA class I or II scheduled to undergo elective operations were classified randomly into 3 groups. Group I and II were injected with thiopental sodium 5.0 mg/kg and midazolam 0.2 mg/kg, respectively. Group III received midazolam 0.1 mg/kg and fentanyl 2 ug/kg. The results were as follows ; 1) The onset time (time from intravenous injection to loss of eyelid reflex) of group III (137+/-10.29 seconds, p<0.05) was longer than those of group I (10+/-3.22 seconds) and group II (37+/-12.49 seconds). 2) The change of the mean arterial pressure : Group III showed minimal change (4% decrease, p<0.05) at 1 minute after endotracheal intubation as compared with group I (21% increase) and group II (6% increase). 3) The change of the heart rate ; Group III showed the least change (6% increase, p<0.05) at 1 minute after endotracheal intubation as compared with group I (18% increase) and group II (12% increase). From these results, it is suggested that the combined use of midazolam and fentanyl may cause less effect on the cardiovascular system during endotracheal intubation than midazolam or thiopental sodium alone.