The hypnotic effects of Zopiclone, a novel cyclopyrrolone derivative, were compared with placebo in a double-blind randomized crossover study in insomniac patients. Subjective morning assessments by the patients showed that Zopiclone 7.5 mg improved the quality of sleep, with a reduction in the sleep onset latency and the number of nocturnal awakenings. Zopiclone was judged by the physicians to be superior to placebo and was preferred by the patients. Subjective residual effects and adverse reactions were minimal.