In the last years, a special progress has been made in understanding of hypothalamicnuclei importance in the regulation of vegetative functions, metabolic processes, and theblood pressure regulation. Due to the using of immunohistochemical and molecular genetic methods, it has become possible to study not only the morphology of neurosecretorycells, but also their connections with other brain regions, both the hypothalamus and thewhole brain.These methods also give an opportunity to identify the neurohormones, synthesized inthem, the places of their primary localization, the ways of their transport and secretion. Itis already well known that the increase in the functional activity of the nervous systemwill be manifested with the cytochemical restructuring of plastic and energy metabolismin the neurons, an increase in the cells' and their intracellular structures size, as well aswith an increase of RNA concentration and content.The objective was to determine morphodensitometric peculiar features of ARChypothalamic nucleus neurons in arterial hypertension with different pathogeneticmechanisms.Material and methods. To achieve the goal we used 3 groups of rats, 10 animals in eachone. The first group consisted of Wistar rats with normal blood pressure, the second groupof rats - with simulated endocrine-salt arterial hypertension (ESAG) - that is correspondent to secondary arterial hypertension in humans caused by endocrine disorders, thethird group - rats of the SHR line - that simulates primary (essential) arterial hypertension in humans. To determine the morphodensitometric characteristics of hypothalamic ARC neurons' nuclei 5 ?m sections of ARC hypothalamus were stained withHalocyanine-chromic alum according to Einarson. Then digital data were processedusing Image J program and morphodensitometric parameters of hypothalamic ARCneurons' nuclei - RNA content, RNA concentration and nucleus area were calculated.Statistical analysis was performed by EXCEL-7.0.Result. It has been established that the formation of arterial hypertension leads tochanges in the morphodensitometric characteristics of the hypothalamic ARC neuronsnuclei. Differences in nuclear area, RNA concentration and content in ARC neuronsdepend on the ethiology and pathogenesis of arterial hypertension. In the model ofessential arterial hypertension, reliably high values of the neurons nuclei area areobserved while the concentration of heterogeneous RNA decreases. In secondary arterialhypertension associated with endocrine disorders, the area of the neurons nuclei, in contrast, decreases with decreasing RNA content and concentration.