Heat shock proteins 70 kDa (HSP70) protect intracellular proteins from the damaging effects ofstress factors of various natures. Moreover, HSP70 play an important role in the vital activity of cells under normalphysiological conditions, performing chaperone functions. These functions are realized in the intracellularspace; however, in some cases, these proteins are also found on the cell surface and in the extracellularenvironment. The causes and mechanisms of HSP70 translocation to the cell surface and secretion into theextracellular space have not yet been well understood, but such an unusual localization of HSP70 activates theimmune system. The surface HSP70 and their extracellular pool stimulate the cytotoxic activity of NK cells.However, direct experimental evidence for the internalization of HSP70 molecules by NK cells has not yetbeen demonstrated. This paper presents the results of the interaction of the extracellular HSP70 pool with NKcells from the peripheral blood. The results demonstrated the confirmation of the internalization of exogenousHSP70 molecules by NK cells. To this end, fluorescently labeled recombinant stress-inducible human HSP70were obtained. The electrophoretic data indicated the absence of protein degradation during the labelingprocess, the purity and stability of the modified protein. To assess the interaction of HSP70 with NK cells, thefluorescently labeled HSP70 was added to an in vitro culture of NK cells isolated by magnetic separation fromthe peripheral blood mononuclear fraction and analyzed by confocal microscopy. This analysis indicated thatliving NK cells internalize extracellular HSP70 with localization both in lysosomes and in phagosomes. Ourexperiments illustrated for the first time the process of penetration of the extracellular form of HSP70 intothese cells. The results suggest that the activation of NK cells under the action of exogenous HSP70 could beassociated with the internalization of these protein molecules.