The interaction of cells with collagen has previously been demonstrated to be of importance in the growth and differentiation of various cells (reviewed by Hay 1981; Kleinman, et al 1981). Chondronectin has been demonstrated to be involved in mediating the interaction of chondrocytes with their matrix. Unlike fibronectin, which binds directly to collagen before the cell can interact with this macromolecular complex, chondronectin must interact with cartilage proteoglycan monomer in order to function efficiently as an attachment factor. Figure 4 is a schematic representation of the interaction between chondrocytes and their matrix components. We suggest that if these specific interactions are perturbed by the introduction of some outside factor, the phenotypic expression of the cells could be altered. For example, chondrocytes are not normally associated with fibronectin (Dessau, et al 1978; Stenman, Vaheri 1978). However, if chondrocytes are grown in the presence of fibronectin they will become more fibroblastic and stop making the cartilage-specific molecules of type II collagen and cartilage proteoglycan (Pennypacker, et al 1979; West et al 1979). Consequently, it is possible that the specific interactions seen between chondrocytes, chondronectin, type II collagen, and proteoglycan may be essential for the maintenance of the chondrocyte phenotype.