Mesenchymal stem cells enzymatically isolated from human placenta were labeled with magnetic fluorescent microparticles (d=0.96 μ). We showed that microparticles in high doses (>10 μl stock suspension per 1 ml culture medium) significantly inhibited cell proliferation in culture. In our work we determined the optimal concentration of particles not affecting physiological properties of mesenchymal stem cells: it does not change cell proliferation, does not induce apoptosis, and does not modulate their transdifferentiation into neuronal cells. In vivo experiments showed that the chosen particles allow easy visualization of transplanted cells ex vivo on sections of different tissues.