Ketamine was administered to 18 baboons (Papio papio) to disrupt epileptic discharges elicited through intracarotid air injection. Discharge suppression was obtained in all animals but could be preceded by a phase of enhancement of the epileptic patterns, which rendered necessary the injection of a supplementary dose. The mechanisms of Ketamine action are discussed, in connection with data from the literature. Some of the latter suggest that its use in proved epileptics facilitates paroxystic patterns or even convulsions while others emphasize its antiepileptic action. Present data corroborate the ambivalent action of this drug. However, its dominant depressant effect obtained with increasing doses is somewhat favourable to its administration to epileptic patients.