The effects of acute administration per os of 30 mg camazepam and the same dose of temazepam, were compared with placebo in 8 young male volunteers, fully adapted to the laboratory environment by 6 nights of adaptation. The study was double-blind, in a random order, 10 days separating each session. Spectral analysis was performed on the all-night records (1-min epochs), and the relative power of six frequency bands calculated. Concerning sleep parameters, temazepam induces a statistically significant reduction of: phase shifts; number of awakenings; percent duration of sleep stages I and IV. A significant increase of the percent duration of stage II and sleep efficiency was also found. Camazepam shows modification, with the same trend, but not reaching statistical significance. Concerning spectral analysis, temazepam induces a light increase of the relative power of the slowest frequencies, paralleled by an increase of the fast bands, while major effects are found on the characteristic periodicity of delta activities, which appear disrupted by the drug. These effects are not evident with camazepam, which does not seem to distort the normal sleep pattern.