Polyethylene fibres of various draw ratio up to 30:1 have been crosslinked by electron beam irradiation in acetylene. The gel fraction increased with dose and showed a significant increase with draw ratio above 10:1. The fibres were examined by differential scanning calorimetry, dynamic mechanical analysis and X-ray crystallography. Fibres of higher draw ratio showed a sharper decrease in melting temperature with dose, ascribed to crosslinking at fold surfaces and greater chain scission, due to higher crystallinity. The main finding was that crosslinking increases the -50-degrees-C dynamic storage modulus at intermediate draw ratio (10:1), but not at low or high draw ratio. The results were interpreted via the random intercrystalline bridge model, which suggests that at 10:1, there is good interlamellar contact but very few intercrystalline bridges. The crosslinking can therefore link together adjacent lamellae at fold surfaces and hence provide crystalline continuity, increasing the modulus.