Bone morphogenetic protein-4 (BMP-4) is one of nine structurally related BMPs belonging to the transforming growth factor-beta (TGF-beta) superfamily of secreted proteins. The human BMP-4 shares 98 % sequence indentity with mouse BMP-4. Mature BMP-4 is a dimer that binds to a multimeric transmembrane receptor with serine/threonine kinase activity. BMP-4, a stimulator of chondrogenesis, both in vitro and in vivo, is a potential therapeutic agent for cartilage regeneration.