SummaryA double-blind controlled trial of two benzodiazepine tranquillizers is described. Seventy-three patients suffering from uncomplicated anxiety states were included in the trial. The drugs concerned were lorazepam in three dosages 0.5 mg., 1.0 mg., and 1.5 mg., compared with diazepam and a placebo, each dosage being administered three times a day. Statistical analysis suggested that lorazepam in 1.0 and 1.5 mg. dosages was superior to diazepam (5 mg.) and placebo, and that the most effective dosage was 1.0 mg. Side-effects were similar in all groups, and generally mild.