The electron spin echo (ESE) method has been used to investigate free radicals in irradiated polymers. The form of the ESE spectra has been found to depend on different parameters (time between first and second impulses; amplitude of the SHF field; concentration of radicals; positioning of the excitation impulse on the absorption line; temperature; and structure of the radicals) in the case of all the polymers studied (polyethylene, deuteropolyethylene, polypropylene, deuteropolypropylene, polyethylene glycol); this fact is connected with differences in the phase retention times at the various sections of the absorption line. At low radical concentrations (10 17–10 18 cm −3) the decay in the ESE signals is determined by electron-nucleus interaction.