EEG effects of zopiclone (7.5 mg), a cyclopyrrolone derivative with hypnotic action, were compared with effects of diazepam (10 mg). Multichannel EEG recordings, double blind crossover trials with placebo, and oral single doses were used in healthy volunteers. Vigilance controlled EEG before and after zopiclone (and placebo), and before and after diazepam (and placebo) were analyzed into FFT power spectra. Effects were assessed as placebo referred pre post medication power differences in four frequency bands. Overall statistics showed significant ) global differences between medication effects in the delta frequency band (0.5 3.5 Hz). After zopiclone, fronto central delta increased bilaterally, whereas after diazepam delta decreased over centro parietal to right temporo occipital regions. These spatially different brain electric effects show that different neuronal populations must have become active in response to zopiclone and diazepam.