Elastin is synthesized by fibroblasts and chondroblasts in cell culture shortly before the cells become confluent. Fibroblasts secrete elastin into the medium as soluble tropoelastin molecules, which form desmosine crosslinks and become constituents of the cell layer only after three weeks in culture. Even then only a small fraction of the available tropoelastin molecules from crosslinks. Conversely, the chondrocytes secrete an elastin which never reaches the media as soluble elastin in significant quantities. Crosslinking occurs immediately in the chondroblast cell layer forming stable, insoluble elastic fibers. Both cells in culture produce lysyl oxidase at approximately the same levels. The reason for the marked differences between these cells in the mode of conversion of soluble elastin to insoluble elastin is not known. The suggestion of Mecham that the extracellular matrix may play a major role in the development of elastogenesis may provide an answer.