The effects of ethanol on the frontoparietal EEG were studied in acutely prepared immobilized cats. Animals with intact brains as well as isolated forebrain preparations (telencephalon and diencephalon intact; brain stem detached by means of a precollicular transection) were investigated. Taped EEG samples of 17 sec duration selected and digitized by a Classic LINC computer. Frequency spectra were computed for frequencies from 0–29 Hz, using the Cooley-Tukey algorithm. In animals with intact brains, intravenous ethanol injections (0.08 g/kg/min) consistently induced a decrease in higher EEG frequencies and an increase of energy in the lower frequency band. The shift toward lower EEG frequencies was also observed in precollicular preparations under the influence of ethanol. Whereas the effect of ethanol on the EEG in the intact brain could be sufficiently explained by its depressant action on the reticular activating system of the brain stem, the profound ethanol-induced changes of the EEG in precollicular preparations provide a basis for the assumption that ethanol also exerts a direct influence upon certain structures of the forebrain.