A single bedtime dose of the benzodiazepine hypnotics, flunitrazepam (2 mg), triazolam (0.5 mg) or flurazepam (30 mg), was administered to young, healthy subjects. Abortive first rapid eye movement sleep (REMS) episodes, characterized by a low level of EEG slow-wave activity (spectral power density in the 0.75-4.5 Hz band) without rapid eye movements and/or muscle atonia, were more frequent in the drug night than in the placebo night or in the drug-free night following upon the drug night. The benzodiazepine hypnotics depressed slow-wave activity in non-REM sleep (NREMS) in the drug night and the subsequent drug-free night. However, the typical declining trend of slow-wave activity over the first three NREMS-REMS cycles, and the cyclic ultradian pattern of slow-wave activity were little affected by the hypnotics. The results indicate that benzodiazepine hypnotics depress the generation of slow EEG waves without disrupting the homeostatic and ultradian processes of sleep regulation.