Benzodiazepine derivatives, chlordiazepoxide(Librium), diazepam(Valium), nitrazepam(Mogadon) and oxazepam(Serenid-D) are mainly used as hypnotics at present. Diazepam has been used mainly for premedication in anesthesia and as an intravenous anesthetic agent. The pharmacological actions of these drugs are tranquilizing effects for central nervous system, slight depression on the cardiovascular and respiratory system, anticonvulsant, anxiolytic and antidepressant effects. A new benzodiazepine derivative, Flunitrazepam(Ro 5-4200) has strong hypnotic action, is anticonvulsant and antidepressant in spite of slight depression of the cardiovascular and respiratory systems. Furthermore the onset and duration of this drug are shorter than the others. In our clinical study, flunitrazepam in the dosage of 0.005mg/kg was administered intravenously, as an intravenous anesthetic induction agent, for 22 surgical adult patients. In each patient, the blood pressure, pulse rate, respiratory rate, minutes volume and arterial gas study were done, before and after administration of the Ro 5-4200. The results are as follows; 1. Dosage of this flunitrazepam is not constant as other benzodiazepines. 2. The effects of flunitrazepam on the cardiovascular system showed slight depression but no effect by one hour post-operation. 3. In respiratory system, the minute volume was depressed slightly and the respiratory rate was increased but negligibly. 4. Undesirable side effects attributed to this drug were not found, except the developing of cough (one case).