Tachycardia and hypertension are well documented complications of laryngoscopy and tracheal intubation in normal patients(Reid and Brace, 1940; Burstein et al, 1950; King et al 1951; Takeshima et al, 1964; Forbes and Dally, 1970). This phenomenon has been studied in detail in cats by Tomori and Widdicombe(1969), who found it to be associated with an increased impulse traffic in the cervical sympathetic efferent fibers. This nervous activity was especially increased by stimulation of the epipharyngeal and laryngopharyngeal regions, and was accompanied by the largest hypertensive response(Takki et al, 1972). Also various arrhythmias were elicited by vagal stimulation during endotracheal intubation(Burstein et al, 1950: King et al, 1951; Forbes et al, 1970), and it has been known that cardiac arrest could be observed in severe cases(Burstein et al, 1950; Dwyer, 1953; Raffan, 1954; Lander and Mayer, 1965). That hypertension during induction of anesthesia in critically ill patients may be harmful is substantiated by reports of cerebral hemorrhage, left ventricular failure and life threatening cardiac arrhythmia(Forbes and Dally, 1970; Dingle, 1966; Masson, 1964; Katz and Bigger, 1970). Pharmacologic attempts to attenuate these blood pressure and heart rate elevations and appearances of arrhythmia have been tried but theese approaches have been only partially successful. We selected at random 60 adult patients who had received operation under the general anesthesia with intubation at Severance Hospital from August to September, 1979. They were divided into 4 groups. Group l was normotensive without trimethaphan(n=20), Group ll was normotensive with trimethaphan(n=20), Group ll was hypertensive without trimethaphsn(n=10) and Group lV was hypertensive with trimethaphan(n=10). The changes of arterial blood pressure and pulse rate, and appearance of arrnythmia were analyzed and data were compared between groups. The results were as follows; 1. In the trimethaphan injected group, during induction attenuation of increase in blood pressure was not significant in the normotensive group but was statistically significant in the hypertensive group. 2, The effects of trimethaphan on changes of pulse rate were not significant during laryngoscopic insertion under general anesthesia. 3, On EKG of hypertensive patients the trimethaphan injected group revealed fewer abnormal EKG findings than the control group. It is suggested from the above results that intravenous injection of a small amount(0.1 mg/kg) of trimethaphan in a hypertensive patient just before endotracheal intubation can be used as one method to prevent a dangerous hypertensive crisis.