The effects of ionizing radiation on ethylene-propylene copolymer were evaluated over the range of total gamma doses up to 500 kGy. The influence of the irradiation dose was investigated by oxygen uptake and thermal analysis. Four testing temperatures (170, 180, 190, and 200 degrees C) and two heating rates between 2.9 and 5.9 K/min were selected for oxygen uptake measurements and thermal analysis, respectively. The competition between crosslinking and scission was examined on the basis of kinetic parameters of postirradiation oxidation. The influence of the momentary concentration of hydrocarbon free radicals is discussed in regard to the contribution of the antagonistic processes of crosslinking and oxidative degradation.