Insulin like growth factor binding protein 4 (IGFBP4) is produced from a DNA sequence encoding the human IGFBP4 protein. Mature human IGFBP4 has a calculated molecular mass of approximately 26 kDa. Due to glycosylation, the recombinant protein migrates as a 32 kDa and 25 kDa protein under reducing and non reducing conditions, respectively. Human IGFBP4 has a potential N-linked glycosylation site and shares approximately 90% amino acid sequence identity with both mouse and rat IGFBP4. IGFBP4 is a member of the superfamily of insulin-like growth factor (IGF) binding proteins which include six high affinity IGF binding proteins (IGFBP) and at least four low affinity binding proteins referred to as IGFBP related proteins (IGFBPrP). IGFBP4 functions as an inhibitor of IGF action and its main function may be to protect cells from overstimulation by IGFs or to allow activation of alternate transmembrane signaling pathways that are inhibited by IGF exposure. IGFBP4 is expressed in multiple tissues including adrenal, testis, spleen, heart, lung, kidney, liver, stomach, hypothalamus, and brain cortex.