SummaryLorazepam has been studied in 212 patients for use as a night-time sedative and for pre-operative medication. Sixty-four of the patients participated in an open pilot trial using lorazepam, and 148 patients formed part of a double-blind trial of lorazepam and diazepam. Each patient was given 2 mg. lorazepam the night before or 2 hours before surgery was anticipated.In the open trial, 68% of patients were asleep within 1 hour of lorazepam administration; only 14% required a repeat dose. The figures for the double-blind trial were 73% and 9% respectively. Over 90% had a continuous relaxed sleep. Muzziness the following morning was the commonest side-effect. The tranquillizing effect of lorazepam was noted following the pre-operative dose in 81% of patients from the double-blind trial and in 85%, of patients from the open trial. In addition, a soporific effect was produced for a period of 3 to 4 hours. The large majority (83%) showed no signs of catecholamine release.