Venlafaxine, a member of a novel chemical class, phenethylamines, is a new antidepressant that inhibits neuronal uptake of serotonin, norepinephrine, and dopamine (in decreasing order of potency) at doses of 75 to 375 mg per day. Depression and antidepressant drugs are known to modify human sleep patterns. Our objective in this double-blind, placebo-controlled study was to assess the effects of venlafaxine on polysomnographic variables by comparing the effects of venlafaxine and placebo on sleep (hypnographic and all-night electroencephalographic [EEG] spectral analysis) and clinical measures (Hamilton Rating Scale for Depression [HAM-D], Montgomery-Asberg Depression Rating Scale [MADRS], and Clinical Global Impressions [CGI]) in inpatients with major depression (DSM-III-R). Following a 7- to 13-day placebo washout period, patients were randomly assigned to receive either placebo or venlafaxine (maximum dose 225 mg/day) for up to 29 days. Sleep evaluations took place at baseline (3 nights immediately before entering the double-blind phase), after 1 week of treatment, and after 1 month of treatment. Sleep stage parameters and all-night spectral parameters were first tested by analysis of variance for repeated measures and then, if indicated, by two-tailed Student t-test. The results on psychiatric rating scales showed improvement from baseline in both treatment groups at all time points, with improvement tending to be greater in the venlafaxine group. Venlafaxine induced a decrease of sleep continuity (decreased total sleep time and increased wake time), an important increase in the onset latency of rapid eye movement (REM) sleep, and a decrease in total REM sleep duration. All-night sleep EEG frequency structure was not modified significantly by venlafaxine treatment as compared with placebo. In conclusion, venlafaxine, despite its novel chemical structure, shows a sleep profile comparable with that of most classical antidepressants.