Midazolam, a new water-soluble benzodiazepine, was investigated as an intravenous anaesthetic agent in 260 adult patients in doses ranging from 0.15 to 0.5 mg/kg using a variety of premedications. Its onset of action was generally slow, taking up to 3 minutes to exert its maximum effect. A wide variability in response was found in that some unpremedicated patients were satisfactorily anaesthetised with 0.15 mg/kg while other were only moderately sedated following doses of 0.5 mg/kg. Less variability was found in the elderly who also required smaller doses. Narcotic premedication potentiated the sedative effect of midazolam. Few respiratory or cardiovascular effects were noted apart from hiccough following the larger doses. The incidence of venous sequelae was much lower than that found following diazepam.