The effects on sleep of a putative hypnotic, benzodiazepine (doxefazepam), were studied in 7 healthy volunteers. Subjects were administered placebo or the active compound at 10-, 20-, and 40-mg oral dose prior to 13 consecutive nights during which they slept in the EEG laboratory. Full-night EEG recordings were obtained, and the hypnogram was determined. The subjective characteristics of sleep (quality, dreams, etc.) were defined by self-administered rating scales; neuropsychological and quantitative waking EEG measurements were performed before drug/placebo administration and in the morning following the final awakening, in order to identify possible signs of 'hangover'. Volunteers thereafter slept at home for 15 nights, self-administering 10 mg doxefazepam each night, and returned to the laboratory for 2 additional full-night sleep recordings. The drug plasma concentration was monitored during the study. Doxefazepam (10 mg) reduced the number of intermediate awakenings and the shifts between distinct sleep phases; single 20- or 40-mg doses or a 2-week administration of 10 mg doxefazepam increased significantly the total sleep duration and the percent duration of the phase 2 and the synchronized sleep and decreased the percent duration of phase 1 and of the intermediate awakenings. Volunteers reported an improvement in the subjective 'quality' of sleep, while evident signs of 'hangover' were not observed. The compound appeared to be of potential use as a sleep regulator.