The models used in magnetopneumography and in cytomagnetometry to estimate the intracellular viscosity and the energy of the cell motiliy are tested with monodisperse and with polydisperse ferrimagnetic micro particles, suspended in highly viscous Newtonian solutions. Using polydisperse particles deviations from an exponential decay were measured. In relaxation and in viscosity measurements the particles behave with an increased hydrodynamic volume.