he aim of study was to identify a response of the thymus CD68+ cells population to the introduction of tautomeric forms of magnesium orotate under magnesium deficiency.Material and methods. Magnesium-deficient status in rats was simulated by furosemide loading (30 mg/kg 14 days); then the animals were injected magnesium orotate in the initial oxo-form (Magnerot©, Vervag, Germany) and hydroxy-form obtained by mechanical activation, dosage 50 mg/kg, for 14 days., The density of thymocytes and macrophages was calculated in the subcapsular zone, cortex and brain matter (stained with hematoxylin and eosin) in the thymus, macrophages were studied immunohistochemically using monoclonal CD68 antibodies (Clone PG-M1).Results. The oxo-form of the drug was shown to lead to an increase in the number of CD68+ cells in the cortex of thymus (1.7 compared with the control) and medulla of thymus (2.3 times), an increase in the intensity of immunofluorescence (22.5%), the appearance of the thymus lobule of large CD68+cells in the cortex and the medulla part with a clearly traced intracellular localization of granules. The introduction of mechanically activated hydroxyl-form was accompanied by an increase in the number of CD68+ macrophages in the cortical area (1.5 times), and cortico-medullary partition (in 1.4 times), but did not affect the cerebral area of the thymus. The overall intensity of fluorescent staining reduced to 27.87±2.2 relative units (RU).Conclusion. The tautomeric forms of magnesium orotate have a diverse effect on the macrophage population of the thymus: the introduction of the oxo-form is accompanied by a significant activating effect on the CD68+macrophages in contrast to the hydroxyl form having a moderate modulating effect.