Platelet-derived growth factor (PDGF) belongs to the family of growth factors consisting of four secreted extracellular ligands including PDGF-A, -B, -C and -D. These isoforms, PDGF-AA, PDGF-AB, PDGF-BB, PDGF-CC and PDGF-DD, act via two receptor tyrosine kinases, PDGF receptors alpha and beta. PDGF isoforms stimulate growth, survival and motility of mesenchymal cells and certain other cell type. They have important functions during embryonal development and in the control of tissue homeostasis in the adult. PDGF-BB is one of the most recently studied isoforms and it plays an important role in skeletal development. PDGF-BB stimulates cell-mediated collagen gel contraction. PDGF-BB modulates endothelial proliferation and angiogenesis in vitro via PDGF beta-receptors.