Various methods exploiting labels or probes are widely used in the investigation of the structure and dynamics of biological systems, including the nitroxide label and probe method. Such investigations are carried out mainly at 3-cm waveband. Up today, however, the EPR spectra of organic free radicals are registered in a narrow range of magnetic fields at this band. This leads to a poor resolution of radical multicomponent spectrum or sum spectra of different radicals and to the ambiguity of the obtained data interpretation. The efficiency of the method was shown to increase considerably at 2-mm waveband mainly due to a higher spectral resolution and lower interaction between spin-packets. The applicability of a new 2-mm waveband EPR spectroscopy for investigation of structural, conformational and dynamic characteristics of different spin-modified biological systems is discussed. The polarity of the microenvironment and the mechanism of molecular reorientation in these systems were determined. High resolution EPR technique combined with the method of steady-state saturation and saturation transfer allows one to analyze separately the electron relaxation and anisotropic very slow molecular librations in biological objects. The possibility of identification of different radicals with close magnetic parameters and charge transfer mechanism in the systems is shown.