Background. Adaptation of the organism to the action of certain damaging factors, including radiation, is closely related to the state of the hypothalamic-pituitary-adrenal system. The important role in its activities is played by adrenocorticocytes (ACC) — the cells of the fascicular zone of the adrenal cortex. The disturbance of the structure and function of these cells can significantly impair and limit the development of the adaptive reactions in the body. One of the most promising ways to prevent the post-radiation changes in adrenocorticocytes consists of the application of the non-pharmacological therapeutic factors, such as low-intensity electromagnetic radiation (EMR) of ultra high frequency ( UHF) and the low-frequency (LF) magnetic field (MF) of low intensity (LI) after the exposition of the cells to the action of radiation. Aims. The objective of the present study was to identify the ultrastructural regenerative — adaptive changes in ACC of the fascicular zone of the adrenal gland in response to the primary preventive action of ultra high frequency EMR, microwave oven, and low-intensity MF after the exposition of the cells to the action of radiation. Materials and methods. The investigations were carried using the outbred male rats (180—200 gr body weight). The experimental animals were allocated to four groups two of which had been preliminarily treated by the application of ultra high frequency EMR and low-intensity MF and were thereafter exposed to radiation. The animals of the third group were exposed to radiation alone without the treatment with the therapeutic physical factors and served as controls whereas the animals of the fourth group underwent no treatment whatever and were regarded as intact. Transmission electron microscopy was used to count light and dark adrenocorticocytes of the fascicular zone. The morphometric analysis of mitochondria included the determination of their number, the average and the total area per standard cell area, and the number of cristae per average area of mitochondria). In addition, the analysis of the lipid content and protein-synthesizing organelles was performed. Results. The study has demonstrated that the primary prophylactic application of ultra high frequency EMR and the low-frequency MF caused stimulation of the cellular and intracellular regenerative-adaptive reactions and increased the resistance of the ultrastructure of ACC in the fascicular zone of the adrenal glands to the action of radiation. These changes were most pronounced in response to the application of ultra high frequency EMR. The resulting structural-adaptive rearrangements of the organelles (the enlargement of mitochondria with the simultaneous increase in the number of cristae, hyperplasia of ribosomes and smooth endoplasmic reticulum, preservation of membranes) were largely due to antioxidative and membrane-stabilizing effects of low-intensity electromagnetic radiation of ultra high frequency and were directly related to the formation of the mechanisms of ACC radioprotection. The Increased regenerative-adaptive potential of these cells prevented the development of the dystrophic processes and protected the adrenocorticocytes from aggressive radiation. Conclusions. The results of the present study suggests the necessity of the further studies on the action of the non-pharmacological therapeutic factors, especially low-intensity electromagnetic radiation (EMR) of ultra high frequency and the low-frequency magnetic field of low intensity as the tools for the prevention of post-radiation changes in the adrenocorticocytes of the fascicular zone of the adrenal cortex exposed to the action of radiation.