120 patients scheduled for total hip arthroplasty were randomized to one of four different groups of bearing surfaces. Patients were randomized to one of two femoral head materials - either oxidized zirconium or cobalt chromium - and one of two acetabular component materials - either high-crosslinked or standard ultra-high-molecular-weight polyethylene. The purpose of the study was to compare proximal penetration of the femoral head into the polyethylene at mid-term follow-up (5 years). Results demonstrated no significant differences in proximal wear of the polyethylene between femoral head materials, as compared to the group which received the same acetabular component.