The number of metal-on-metal bearings used clinically continues to increase, particularly in young, active patients. The single greatest concern with the use of a metal-on-metal bearing continues to be the elevated levels of metal ions measurable in patients' blood and urine following implantation. There are multiple complex issues associated with the analysis of metal ions, including collection techniques, analysis, statistical methodologies, and reporting of results. To date, the literature on this topic has been characterized by significant variability in all of these factors. This paper seeks to establish a consensus among 3 investigators who have been working in this area and to offer guidelines on the complex methodology involved in the evaluation of metal concentration in patients following metal-on-metal hip arthroplasties.