The cardiovaseular response evoked by tracheal intubation was observed in 69 patients undergoing elective surgery in whom anesthesia was induced with group A, B and C induction agents. Sixty nine ASA class 1 or 2 surgical patients were divided into three groups. Group A: thiopental 5 mg/kg (control) Group B: thiopental 2 mg/kg with midazolam 0.1 mg/kg Group C: midazolam 0.2 mg/kg Systolic and diastolic blood pressure, mean arterial pressure, heart rate and loss of eyelid reflex were measured in each group. There was a little difference in the cardiovascular changes between group A and C. But there was not a significant difference between group A and B and also between group B and C. The measured time until loss of eyelid reflex of the group C (55+/-30 sec) was considerably longer than other groups (Group A: 10+/-3 sec, Group B: 37+/-13 sec). The incidence of venous complication in three groups was low. Pain on injection and posto- perative nausea and vomiting was noted in one patient of the group A and B respectively, but no patient in the group C. There was no significant difference in the incidence of the postoperative local venous complication. On the whole, these results suggest that the difference between midazolam and thiopental had no apparent hemodynamic change. From the above results, both midazolam alone and midazolam combined with thiopental may be useful agents for induction of anesthesia.