1. The present investigation was intended to examine the effects of the acute administration of several doses of cocaine on sensory evoked responses of freely moving rats. 2. Each structure and each component of the average sensory evoked potentials were affected by cocaine differently. 3. The changes induced by cocaine differ from those observed following other drug treatments. Therefore, it may be assumed that the changes observed are related directly to cocaine. 4. The present observation demonstrated a greater degree of sensitivity to low doses of cocaine than other types of electrophysiological recordings. In general cocaine in the lower doses (0.25 or 0.5 mg/kg) induced an increase in the sensory amplitude response while in the highest dose (10.0 mg/kg) attenuation of the sensory responses was obtained. 5. We assume that the euphoric effect induced by cocaine is due to the potentiation of sensory input within the limbic-hypothalamic system. In higher doses, the fatality caused by the drug may be due to the depression of the sensory input.