A recently developed quantum mechanical approach devoted to the study of structural and magnetic properties of organic free radicals was applied to the lowest triplet state of quinoxaline. From a quantitative point of view, hybrid Hartrec-Fock/Kohn-Sham methods (here B3LYP) confirm their reliability, whereas the Hartree-Fock method gives disappointing magnetic results. From an interpretative point of view, spin polarization effects are well represented by the semi-empirical McConnel relation between spin densities and isotropic hyperfine couplings.