In this brief review the authors endeavored to show how methods developed for molecular studies of the development, onset, and progression of OA have been used to develop biomarker assays that might be of use in the detection of incident OA and in progression of established OA (Fig. 2). These assays involve analyses of specific molecular products in body fluids that result from the cleavage and synthesis of molecules in specific skeletal tissues and from inflammatory processes associated with OA joint disease. These assays are proving to be of value in the detection, study, and treatment of OA, especially with respect to improving understanding of the pathology of the disease and how it can best be detected and managed. Such assays also offer the potential to develop much shorter, more efficient, and cost effective clinical trials for the evaluation of potential disease-modifying therapies for OA.