The integrity of the collagen network and the proteoglycans is essential for the maintenance of the mechanical properties of cartilage. In spite of a slow turnover, cartilage is able to modify the synthesis of its matrix and has reparative powers. Chondrocytes also possess the enzymes necessary for degrading the matrix. Most substances which are mediators in the inflammatory process act on cartilage, either by inhibiting synthesis, or by stimulating the enzymes involved in degradation. The multiplicity of the mediators (kinin, histamine, serotonin, complement, free oxygen radicals, pharmacologically active lipids, cytokinin) and the interactions among the various systems that are called into play account for the difficulties encountered in treatment.