Determinations of glutamate dehydrogenase (GDH), glutamic acid decarboxylase (GAD), and GABA aminotransferase (GABA-T) in the epileptogenic (cobalt) mouse cortex revealed a fall in the activities of GDH and GABA-T and an increase in GAD. However, of the three enzymes, only changes in GDH appeared to coincide with the entire period that animals were epileptic. The decrease in GABA-T was observed in the first week following the onset of cobalt-induced epilepsy but the activity of this enzyme had returned to normal before all epileptic signs had disappeared. On the other hand, the rise in GAD activity was observed 3–4 days after epilepsy had become established. Injections of taurine to animals did not influence the above findings but might have slowed recovery to normal enzyme values.