45 subjects aged over 65 years were randomly assigned to treatment with lormetazepam 0.5 mg or 1 mg or placebo. Mood and performance were measured with a battery of computerized tests. Subjects were tested before and after 1 and 8 nights of treatment. Pre- and post-treatment scores were analysed by a multivariate covariance technique, the pre-treatment score serving as covariate. The single and repeated doses of lormetazepam resulted in impairment of performance in a memory task, and the repeated dose administration impaired performance of a perceptual task. The single administration of a low dose gave an improvement in fine motor control. No change was found in the mood states of the subjects. © 1991 Springer-Verlag.