RO 21-3981, a new water soluble benzodiazepine, was studied in 24 patients both as an intravenous premedicant and to induce anesthesia. The premedicant dose of 5 mg produced lack of recall and marked sedation within 1 to 2 minutes after injection and persisted for at least 32 minutes. Subsequent induction of anesthesia required an additional 5 to 25 mg of RO 21-3981. However, anesthesia was not induced in 1 patient with 25 mg and was accomplished only with inhalation anesthesia. Loss of lid reflex was unreliable as a sign of induction for patients in whom tracheal intubation was planned. Although decreases in blood pressure of 10 to 30 mm Hg were noted after administration of RO 21-3981, systolic pressure was not recorded below 90 mm Hg. RO 21-3981, because of its amnesic, sedative, and anxiolytic properties, appears to be an excellent premedicant although the 5 mg dose studied was probably larger than necessary. For induction of anesthesia, RO 21-3981 may be an effective alternative to thiopental.