The presence of oxygen had a varied effect on the gamma-radiolysis of the amorphous copolymer, poly[tetrafluoroethylene-co-perfluoro(methylvinyl ether)] (TFE/PMVE), depending upon radiolysis conditions. Radiolysis undertaken in stages, up to a dose of 1500 kGy (1 rad = 10(-5) kGy) in the presence of air, resulted predominantly in chain scission and a wax-like substance was produced; whereas, other studies have shown that continuous radiolysis of the polymer produced a crosslinked network. Radiolysis of semicrystalline TFE/PMVE in vacuum up to a dose of 4200 kGy produced little change in the crystalline content. Crosslinking, however, predominated in the amorphous regions, which had the effect of lowering the crystallization temperature upon cooling from above the crystalline melt.