The effects of fluoxetine on automated measures of electrooculographic (EOG) and electromyographic (EMG) activity were evaluated in 41 patients with nonpsychotic, major depressive disorder. Sleep EEG evaluations were conducted at baseline, while patients were symptomatic and unmedicated, and following four to five weeks of treatment with fluoxetine (20 mg). The number of eye movements (> 75 microV) and the amplitude of EOG and EMG activity increased significantly on treatment in REM, stages 1, 2, and slow-wave sleep. All patients showed EOG and EMG abnormalities in at least one stage of sleep. Thirty-four percent of patients showed increased EOG and EMG activity on treatment in every sleep stage. It is suggested that fluoxetine-induced oculomotor abnormalities are likely to be the result of increased availability of serotonin and secondary dopaminergic effects.