The compounds of formula RFe_12-xM_x with R = rare earth, M = d-metal and their interstitial derivatives, generally exhibit ferro- or ferrimagnetic properties. Preliminary EPR analyses performed on ErFe_12-xMn_xX_y (x = 5, 4, 3; X = H, C) and NdFe_10.7V_1.3C_y (y = 0, 1) are reported. A direct correlation between the different types of electron resonance traces and the bulk magnetic properties is established, clearly revealing the ferromagnetic and the paramagnetic domains of the magnetic diagram of phases. No spin reorientation transition (SRT) was evidenced for any of the studied compounds.