This study shows that toxic effect of non-modified nanoparticles of Fe3O4 in vitro depends on metabolic and morphological condition of cells, derived from fetuses and newborn rats. During the cultivation of cells with magnetic nanoparticles, the new-born rats. During the cultivation of cells with magnetic nanoparticles, the latter bind to the cell surface and penetrate into the intracellular space. In this case, sorption of nanoparticles on the cell surface makes it difficult for cells to adhere to substrate, and the absorption by spread cells may prevent their proliferation. Magnetic nanoparticles are well absorbed by the upper layer of cellular aggregates. In this case, the cells of the inner layer remain intact. Consequently, the cell aggregates are able to respond to the constant magnetic field. These aggregates could potentially by used in cell transplantation for directed cell delivery.