The purpose of this study was to evaluate the short- and intermediate-term (21 days) effectiveness, as well as the carryover and withdrawal effects of 7.5 mg of zopiclone, a new short-acting hypnotic agent. 6 patients with chronic insomnia, ranging in age from 33 to 57, participated in the study. Both EEG sleep recordings and subjective rating scales were used to evaluate the drug. Zopiclone increased the total sleep time throughout its 3-week administration period although only during the short-term period was this increase statistically above baseline. There was no carryover effect nor rebound insomnia upon drug withdrawal. The drug significantly increased the duration of stage 2 sleep, decreased stages 3 and 4 sleep, and had no effect on the duration of REM sleep. There were no reported side effects.