Disturbances in GABA-ergic inhibitory system were noted upon the exposure of thalamus and hypothalamus of experimental animals to stress of 18 hours and longer duration but not of 3 hours duration. Phenibut (I mg/kg) eliminates the symptoms of GABA-system disturbances revealed upon exposure to stress, decreases the tension of stress reaction and hyperglucocorticoidemia which causes hyperglycemia. In the bodies of intact rats phenibut causes "switching on" of adaptive GABA-system function, which is more physiological than the one appearing on short-term stress.