The influence of cross-linking on fracture properties of polyethylene has been studied by the method of essential work of fracture (EWF). Three distinct values of the cross-link density were obtained by beta irradiation with three distinct radiation doses, and characterized by sol-gel and solvent swelling measurements. EWF tests were performed at speeds of 0.045 to 100 mm min(-1) at 80 and 110 degrees C. The fracture toughness, as defined from the EWF method, is analyzed through essential (w(e)) and nonessential (beta w(p)) components. Both values were found to be decreasing functions of the cross-link density. But cross-linking also suppresses the toughness decrease observed in linear PE at low speeds/high temperatures. It is hypothesized that cross-linking prevents the chain disentanglement that occurs during crack growth. In conclusion, EWF tests performed at low speeds appear as an interesting method to characterize the influence of structural factors on the fracture properties of polyethylene. (c) 2005 Society of Plastics Engineers.