The tolerance of zopiclone, a hypnotic belonging to a new chemical group, the cyclopyrrolones, was studied in a follow-up trial in 23,000 insomniac outpatients treated for 3 weeks. The results from the interim analysis of the first 10,000 cases confirm the efficacy and safety of zopiclone under usual prescribing conditions. The average daily dose of zopiclone was 0.97 +/- 0.21 tablet (7.275 +/- 1.575 mg). The study population included 63.1% of female and 36.9% of male patients; the mean age was 52.3 +/- 16.6 years. 93.1% of the patients completed the trial. 8.2% of the patients experienced adverse reactions which resulted in drug discontinuation in only 2.8% of cases. In the global evaluation, the efficacy was rated excellent or good in more than 80% of the patients.