The effects of orientation by plastic strain on the impact fracture resistance of a pipe-grade polyethylene have been investigated. Isotropic samples of bulk polymer were subjected, by plane-strain compression, to uniform Hencky strains of up to +/- 40%. In some samples this strain was reversed to restore the original dimensions. Impact bend specimens were prepared from samples oriented either normal to or within the fracture plane. Plane-strain fracture resistance and transition temperature were measured at 1 m/s by using the ISO 17281 method, and plane stress fracture resistance was measured by using the Reversed Charpy test. Orientation within the fracture plane by plastic compression across it compromises the relatively high plane-stress toughness of this material and increases the brittle-tough transition temperature, while the opposite is true of plastic extension. Reversion from a state of adverse orientation, by completing a strain cycle, only partially restores the fracture resistance of the isotropic polymer. (c) 2005 Society of Plastics Engineers.