The article concerns biological effects of non-ionized electromagnetic irradiation which is considered in modern world as a serious ecological factor. Influence of decimetric microwave irradiation (460 MHz) on free radical processes in the rat brain tissues--visual cortex and hypothalamus--were investigated. Oxidative effects of both lipid peroxidation and specific activity of glutathione reductase were determined. It is shown that whole body irradiation for up to 4 weeks results in considerable changes of the above indices dependent on the irradiation intensity and age of the animals. Decimetric microwaves have oxidant effects at high intensity irradiation (SAR--15 mW/kg), while these effects are antioxidant at low intensity (SAR--5 mW/kg). Physiological implications of different oxidative metabolic responses of the hypothalamus and the cortex to microwaves irradiation are discussed.