Flunitrazepam (Ro 5–4200) has been studied as an induction agent in 220 volunteers or patients. It was assumed to be 10 times as potent as diazepam. The maximum soporific effect did not occur until 90–120 s after injection. There was great individual variation in response to flunitrazepam and some patients did not lose consciousness even after receiving 6 mg (approximately 0.1 mg/kg). Opiate premedication enhanced its action, but delayed recovery. There was a dose-related increase in minor respiratory upset with flunitrazepam in unpremedicated patients and a high frequency of arterial hypotension following large doses given to patients who had received opiate premedication. Venous sequelae were no more frequent than after comparable doses of diazepam. Flunitrazepam was not a very satisfactory drug for the induction of anaesthesia, and recovery was too prolonged for routine use.