Morphofunctional state of the thyroid and nuclei in the hypothalamic large cells was examined following exposure to ionizing radiation at the dose of 20 Gy without and with ethanol administration (2.25 g/kg) before or after exposure. The highest thyroid radioprotecting effect of the ethyl alcohol was achieved when introduced before exposure as it reduced apoptosis of thyrocytes and balanced the disturbances in colloid amino acids iodination. As for nuclei of the hypothalamic large cells, the radiomodifying effect of ethanol was synergic when introduced before and potential amplifying after the radiation exposure being manifested by distinct activation and ensuing overstrain and exhaustion of the neurosecretory cells. Analysis of the experimental data suggests causality of the thyroid protecting effect of ethanol by functional hyperactivation of supraoptic and paraventricular nuclei in the hypothalamus.