A study was made of the content of gamma-aminobutyric acid (GABA) glutamate and the total of aspartate+asparagine+glutamine, and activity of glutamatedecarboxylase and GABA-α-ketoglutarate aminotransferase in the mouse brain after exposure of head to 1500 R of ⁶⁰Co-γ-rays. GABA content gradually increases shortly after exposure, and glutamate content decreases at later times following irradiation. The activity of both enzymes diminishes: in the case of GABA-transaminase, however, the diminution proceeded slower and lasted longer. The role of shifts in the GABA system in the development of damages to the nervous system after local exposure is discussed.