Six patients between the ages of 25 and 59, with chronic, primary insomnia received the new, non-benzodiazepine, hypnotic zopiclone continuously for 17 weeks after a drug free interval of 12 nights. To qualify for the study, sleep efficiency, determined by a sleep study on two, consecutive, placebo-controlled nights, had to be less than 75%. Patients evaluated their sleep by questionnaire and had sleep studies completed throughout active treatment. Zopiclone (7.5 mg) increased sleep efficiency by decreasing sleep latency, wakefulness after sleep onset and increasing total sleep time. Sleep architecture was minimally affected by zopiclone treatment; no significant changes in delta or REM sleep were observed. The commonest side effect was a bitter or metallic taste. No significant changes in biological functioning were noted throughout the study period. These findings indicate that zopiclone is a safe and effective hypnotic medication which maintains its effectiveness with protracted use.