Superparamagnetic iron oxide nanoparticles, so called SPIONs, are used as tracers in medical imaging, e. g. for magnetic particle imaging (MPI) or magnetic resonance imaging (MRI). Since the half-life time of the SPIONs in the bloodstream is quite short because they are quickly absorbed by the reticuloendothelial system (RES), the particles are introduced into human red blood cells (RBCs) to increase their half-life time in the blood circulation. The hypotonic swelling procedure is used to incorporate the particles into the RBCs. Before the SPIONs are introduced into the RBCs, they are fluorescent labelled. To evaluate the result transmission electron microscopy, magnetic particle spectroscopy and fluorescence microscopy are used. Fluorescein isothiocyanate and rose Bengal were chosen as fluorescent dyes because their biocompatibility is guaranteed. The results suggest that the method hypotonic swelling can be used to successfully introduce the nanoparticles into RBCs and that the magnetic properties of the particles which are necessary for imaging are not influenced.