Ultra high molecular weight polyethylene (UHMWPE) is currently used in artificial joints as the best polymer for bearing against metallic counterparts. It has a low coefficient of friction, a good resistance against wear, and a high toughness. In recent years however, the suitability of this material has been questioned due to the association between implant loosening by osteolysis in the joint vicinity and polyethylene debris. Friction characteristics at polyethylene-prosthesis articular interface influence the state of stress at and around articular regions and consequently the extent of surface damage and wear of both materials in contact. In this investigation, following our earlier bone-implant friction studies [1–3], uni- and bi-directional friction properties of polyethylene-metal interface are measured under different contact pressures and two conditions of wet and dry.