The non-invasive determination of temperature in tissue has been a highly desired technical goal for hyperthermic oncology. In previous work, it has been shownthat electron paramagnetic resonance spectroscopy can be used for non-invasive monitoring of temperature in vivo. Our goals are to optimize the developed method, to combine it with non-invasive oximetry and to apply it to the animal model. The EPR spectrum of nitroxide radicals is strongly dependent on its mobility and orientation relative to the external magnetic field. Both mobility and orientational dependency of spectral parameters can be used to gain information about temperature ifthe free radicals are embedded in a medium that undergoes aphase transition in the temperature range of interest.