Osteoarthritis is a degenerative disease of joint cartilage, characterized by the progressive and permanent degeneration of cartilage due to an imbalance in normal extracellular matrix turnover. Interleukin-1 beta is a proinflammatory agent, which is present in an elevated amount in osteoarthritic cartilage, and is thought to play a decisive role in osteoarthritis. Interleukin-1 beta acts as an important mediator of extracellular matrix changes where its activity is regulated by glycosaminoglycan composition. The aim of this study was to investigate the extracellular matrix changes in bovine cartilage explants following interleukin-1 beta treatment by morphological, histochemical and biochemical methods. Interleukin-1 beta stimulated the release of matrix sulfated proteoglycans in the culture medium, and significantly inhibited sulfated proteoglycan synthesis. These events were associated to a strong stimulation of nitric oxide production. Interleukin-1 beta-treated cartilage showed evident collagen fibers around the chondrocytes, together with diminished glycosaminoglycan sulfate content in the extracellular matrix of the explants. Moreover, the ultrastructure and viability of cells did not change in treated cartilage. Our data show that interleukin-1 beta modifies the ECM turnover without toxic effect on chondrocytes.