Residual sedative effects seem to be intrinsic properties of effective hypnotic agents. Residual effects are dose related and more likely if the elimination half-life is greater than 12 hours. In two separate studies, investigations into effects on performance were carried out using a series of psychometric tests. In the first, a group of skilled radar operators working a shift system were given a pre-sleep administration of temazepam 20 mg and measurements were made of any residual effects. In the second clinical study, general practice patients suffering from idiopathic insomnia were randomized onto either temazepam 20 mg, triazolam 0.25 mg, nitrazepam 5 mg, flurazepam 15 mg, or placebo. Assessments were made using the Leeds Psychomotor Tester to measure Choice Reaction Time and Critical Flicker Fusion. In a separate test, digit substitution was used to measure sensory processing ability. In addition, the Leeds Sleep Evaluation Questionnaire was completed by each patient in the clinical study to provide a subjective evaluation of ease of getting to sleep, ease of awakening and behaviour after awakening. Neither study showed a residual activity that was likely to impair performance following temazepam 20 mg indicating the usefulness of this drug in the management of idiopathic insomnia and sleep difficulties introduced by changes in scheduling of sleep, i.e. intercontinental travel or shift work.