The purpose of this study was to compare the cognitive eect of two medications frequently prescribed to patients suering from insomnia. Using a double-blind design, we evaluated three parallel groups of 20 insomniac patients treated over a period of 3 weeks with zopiclone, temazepam and placebo, respectively. Our hypothesis was that the impact of zopiclone 7 . 5 mg/day on cognitive functioning would be minimal 12 h after administration and that temazepam 30 mg/day would aect explicit memory, as is the case with other benzodiazepines. Patients were assessed at baseline following a 1-week, single-blind placebo-intake period, and again at the end of each of the 3 weeks of the comparative phase. Then, in order to estimate the severity and duration of potential rebound insomnia, patients were again assessed following another 1-week, single-blind placebo-washout period at the end of the 3 weeks of treatment. The overall duration of the study for each patient was thus 5 weeks. The instruments of measure used were the Hamilton scale for anxiety, daily self-rating questionnaire for assessment of sleep onset, duration and quality, and two large batteries of psychometric tests. The ยฎrst of these batteries assessed memory and included span tests for short-term memory, cued recall tasks for long-term explicit memory, and a word-completion task for implicit memory; the second measured attention and concentration through the assessment of alertness, sustained attention and divided attention. The sleep and anxiety results obtained conยฎrm the ยฎndings of previous research. Zopiclone and temazepam possess a clinically signiยฎcant hypnotic activity, with no rebound insomnia or anxiety, during the week of drug withdrawal. The results indicate that the two hypnotic drugs studied have little impact on cognitive functioning. We can therefore conclude that at the doses administered over the 3 weeks, the two hypnotic drugs in question are relatively safe and ecacious in the treatment of insomnia and enable patients to enjoy a good quality of life.