It has recently been reported that chemical evaluations of a new benzodiazepine derivative, flunitrazepam (Ro 5-4200) revealed promising effects as premedicant. We studied on effects of premedication by double blind technique comparing flunitrazepam (Ro 5-4200) 0.03mg/kg I.M. and meperidine HCI 1mg/kg I.M. in 300 cases of preoperative patient by random selection. The questionaire on drowsiness, sleepiness and awareness during transport to the operation theatre, as well as nausea and vomiting were checked by anesthetists who were ignorant of the given premedicant. Following results were obtained; 1) Flunitrazepam has excellent calming effects in preanesthetic period, inducing drowsiness and adequate rest. 2) Flunitrazepam produces good sleep the night before operation. 3) Flunitrazepam has lower incidence of nausea and vomiting than that cf meperidine HCI.