105 patients with unilateral noninflammatory degenerative joint disease were randomized to undergo total hip arthroplasty using either a 28mm metal-on-metal bearing surface, a 36mm metal-on-metal bearing surface, or a 28mm metal-on-polyethylene bearing surface. The purpose of this study was to compare metal ion levels and clinical outcomes between the three treatment groups. Upon analysis, the metal-on-polyethylene group demonstrated significantly lower metal ion levels in serum and whole blood compared to both of the metal-on-metal groups, while increasing metal ion levels over time and higher erythrocyte cobalt levels were observed in the 36mm metal-on-metal group. Mean HHS scores, WOMAC scores, and SF-12 mental and physical scores were similar between all three treatment groups.