Zopiclone (7.5 mg), a cyclopyrrolone derivative with a 6.5 h half-life, and flurazepam (30 mg) were compared to placebo in a randomized double-blind study involving 36 adult patients suffering from insomnia. All previous psychotropic drugs were discontinued 1 week prior to the study. During 4 weeks, 12 patients received zopiclone, 12 flurazepam and the others placebo. Thereafter, all patients received single-blind placebo for 3 nights. Rapidity of sleep onset, sleep duration, frequency of nocturnal awakenings, psychomotor coordination and side-effects were assessed daily with a questionnaire and a symptom checklist. The results of the study suggest that zopiclone 7.5 mg was at least as potent as flurazepam 30 mg in inducing and maintaining sleep. Both drugs maintained their efficacy during the 4 weeks of treatment. However, the two drugs differed in that flurazepam impaired psychomotor coordination whereas zopiclone did not demonstrate daytime protracted effects on psychomotor performance. Upon discontinuation of drug treatment, score values of the different sleep parameters under study returned to the baseline values. Side-effects were mild and consistent with earlier studies.