Inorganic nanoparticles containing rare-earth ions are of particular interest as luminescent contrasting agents for obtaining optical images from the depth of biological tissues. Stable aqueous colloidal solutions of Nd3+: LaF 3 nanoparticles with strong luminescence in the NIR and visible spectral ranges under NIR laser excitation were synthesized by hydrothermal microwave treatment. The results of their luminescence visualization under system-wide administration to laboratory animals with transplanted tumors are presented. The histological distribution of the nanoparticles is verified by laser upconversion microscopy.