A low-field (0.6 Gauss, 2 MHz) EPR spectrometer providing quantitative parameters is described. It gives informations such as frequency dependence of the linewidth, anisotropy of inhomogeneous line and also the values of T1, T2 and the magnetic susceptibility using simple hypothesis.

The behaviour of different typical π-systems, as well metallic as semiconducting is compared to a radical anion salt, quinolinium bis tetracyano-quinodinemethane Qn(TCNQ)2 considered as a reference.

The materials physical characteristics will be provided by a new variable field (0.6–60 Gauss, 2–200 MHz) which is under realization, for an extended family of organic radicals.