Fibroblast growth factors (FGFs) are members of a large family of structurally related polypeptides (MW 17-38 kD) that are potent physiological regulators of growth and differentiation for a wide variety of cells of mesodermal, ectodermal and endodermal origin. FGFs are substantially involved in normal development, wound healing and repair, angiogenesis, a variety of neurotrophic activities, and in hematopoiesis as well as in tissue remodelling and maintenance. They have also been implicated in pathological conditions such as tumorigenesis and metastasis. The FGF family consists of at least seventeen members designated FGF1 through FGF17. To date, four genes encoding for high affinity cell surface FGF receptors (FGFRs) have been identified: FGFR1 [flg-1(fms-like gene 1)]; FGFR2 [bek (bacterial expressed kinase gene product)]; FGFR3 (cek-2) and by alternative splicing have been reported. Soluble, secreted or possibly cleaved forms of FGFR-1 and FGFR-2 have also been found in body fluids or were artificially constructed. An example is a soluble FGF-binding protein containing the extracellular region of FGFR3 and the secreted form of placental alkaline phosphatase (FRAP3). FGFRs are members of the tyrosine kinase family of growth factor receptors. They are glycosylated 110-150 kD proteins consiting of an extracellular domain, a single transmembrane region and a cytoplasmic split tyrosine kinase domain, which is activated following ligand binding and receptor dimerization. The extracellular, ligand binding, region is constructed with either two (beta type) or typically three (alpha-type) immunoglobulin (Ig)-like domains, and an eight amino acid ‘acidic box’. The ligand binding site of all FGFRs is confined to the extracellular Ig-like domains 2 and 3. FGFRs exhibit overlapping recognition and redundant specificity. One receptor type may bind several of the FGFs with a similar affinity. Also, one FGF type may bind similarly to several distinct receptors. This accounts for the rather identical effects of different FGF ligands on common cell types. FGFs binding to cellular FGFRs depend on, or is markedly facilitated by the low-affinity interaction of FGFs with the polysaccharide component of cell surface or extracellular matrix heparan sulfate proteoglycans (HSPG). Signal transduction by FGFRs requires dimerization or oligomerization and autophosphorylation of the receptors through their tyrosine kinase domain. Subsequent association with cytoplasmic signalling molecules leads to DNA synthesis or differentiation. The signalling and biological responses elicited by distinct FGFRs substantially differ and are dictated by the intracellular domain. FGFR3 is widely expressed in many fetal and adult human and animal tissues. The FGFR3 expression profile largely correlates with its tissue specific expression at the mRNA level.