Intraventricular injection of cerebrospinal fluid obtained from cats with electroshock seizures resulted in suppression of generalized picrotoxin-induced seizures in rats. Antiepileptic action of cerebrospinal fluid was abolished by partial bilateral midbrain destruction that included the region of colliculi superii. Electrical stimulation of cerebellum in cats with such destructions caused the appearance of a pronase-sensitive antiepileptic substances in cerebrospinal fluid.