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Adult articular cartilage is sparsely populated by chondrocytes, which are embedded in an abundant extracellular hydrated matrix comprising collagens (predominantly type II with smaller amounts of types VI, IX and XI) (Eyre et al., 1992), proteoglycans (PGs) (predominantly aggrecan with smaller amounts of decorin, biglycan and fibromodulin) and only small amounts of noncollagenous matrix proteins (Heinegård and Rosa-Pimentel, 1992). The collagens are organized into an insoluble fibrous network of high tensile strength, which helps contain the soluble deformable PGs that give the tissue its ability to undergo reversible deformation (Sah et al., 1992). A variety of culture systems has been used to elucidate the complex mechanisms regulating the synthesis of PGs, to examine how these become organized into the extracellular matrix and to learn more about the processes involved in their turnover. For example, much of what we know today con-cerning the structure and synthesis of cartilage PGs was obtained using chondrocytes cultured as high density mono