FGF5, or Fibroblast Growth Factor 5, is a growth factor with a number of biological roles including including cell proliferation, differentiation, repair, migration, and embryonic development. It is also known as heparin-binding growth factor 5, HBGF5, TCMGLY, and Smag-82. FGF5 in humans is a 268 residue secreted protein, with a predicted mass of about 29 kDa. There are reported to be two isoforms. FGF5 regulates hair growth; disrupted expression in mammals results extremely long hair. It was originally identified as an oncogene, containing regions with 40 to 50% homology with FGF1 and FGF2. An immunoassay such as a FGF5 ELISA kit will be a useful tool in identifying the presence or expression of this growth factor.