54 patients suffering from osteoarthritis of the hip were randomized to receive total hip arthroplasty using either metal-on-metal or metal-on-polyethylene bearings. The goal of this study was to determine the plasma concentration of specific metal ions at different post-operative time points for both types of bearings. The results of this study indicated that at 2 year follow up, the metal-on-metal bearing group had significant increases in chromium, cobalt, nickel and manganese, whereas the metal-on-polyethylene bearing group had a smaller increase in cobalt and nickel when compared to pre-operative levels.