Research in the past year on evaluating serum and synovial fluid markers in osteoarthritis has helped to define more precisely how the components of cartilage extracellular matrix correlate with disease progression. Novel, cartilage-specific markers, such as the cartilage oligomeric matrix protein, have been detected in serum and synovial fluid, and their relevance in the pathogenesis of osteoarthritis must now be determined. Precisely defined cartilage matrix protein changes in surgically induced and spontaneously occurring animal models of osteoarthritis have contributed to a better understanding of the dynamics of cartilage and bone reparative and degradative pathways.