Human Platelet Derived Growth Factor (PDGF) is a potent mitogen for a wide range of cell types including fibroblasts, smooth muscle and connective tissue. PDGF is composed of a dimer of two chains termed the A chain and B chain, and thus can be present as AA or BB homodimers or as an AB heterodimer. Human PDGF-BB is a 14-18.0 kDa protein containing 109 amino acid residues.