This study was undertaken to evaluate the effect of flunitrazepam as a premedicant on the prevention undesirable side effects such as hypertension, tachycardia and emergence phenomena associated with ketamine anesthesia. Twenty surgical adult patients were given flunitrazepam(2 mg) and atropine intramusculary before anesthesia. Endotracheal anesthesia was induced by ketamine and alcuronium and maintained with 0.1% ketamine infusion, 02-N2O and alcuronium. The results were as follows. 1) Sedative effect of flunitrazepam as a premedication waa satisfactory in 90% of the patients. 2) Anesthesia was induced smoothly with ketamine(average 0.98mg/kg) and alcuronium (av. 0.33 mg/kg) for intubation. Total dose of ketamine averaged 0.014 mg/kg/min during anesthesia. and was less than that of the Lorazeam group. 3) The influence on blood pressure and pulse rate due to flunitrazepam were not significant but they were increased an average 18 and 16% immediatly after intubation. More than 20% increase from preoperative blood pressure and pulse rate during anesthesia waa noted in 4 and 6 cases respectively. 4) As emergence phenomena, diplopia with moderate delirium and visual hallucination was reported in 2 cases. However unpleasant dreams were not complained of and a long amnesic effect experienced in all cases. From the above results, it may be concluded that, premedication with flunitrazepam and endotracheal anesthesia with ketamine infusion, alcuronium, N20 and 02 can reduce the undesirable effects of ketamine and this is one of the suitable balanced anesthesia techniqes for long operation especially in old, critically ill patients.