High-density polyethylene (HDPE) and low-density polyethylene (LDPE) were irradiated in vacuo at 30-220 and 30-360 degrees C, respectively, with gamma-rays at doses of 10-400 kGy. Temperature dependence of cross-linking and gas evolution was investigated. It was found that cross-linking was the predominant process up to 300 degrees C and the gel point decreased smoothly with temperature. The increase of G(x) with temperature was likely attributed to the temperature effect on addition of radicals to the double bonds present in the polymer. Above 300 degrees C, the gel fraction at a given dose decreased remarkably with temperature and turned to zero at 360 degrees C. The molecular weight variation determined with gel permeation chromatography (GPC) indicated the enhanced degradation at 360 degrees C by radiation. G-values of H-2 increased with temperature and varied with dose. The compositions of the C-1-C-4 hydrocarbons evolved depended on the structures of side branches. Raising the temperature favored the formation of unsaturated hydrocarbons, and the yield of unsaturated relative to saturated hydrocarbons decreased with dose.