Insulin like growth factor binding protein 3 (IGFBP3) 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). The IGFBP members are cysteine rich proteins with conserved cysteine residues clustered in the amino terminal and the carboxy terminal regions of the molecule. The cDNA sequence encoding the mature human IGFBP3 is fused to the signal peptide of CD33. Human IGFBP3 is the major IGF binding protein in plasma where it exists in a ternary complex with IGFI or IGFII and an acid labile subunit. IGFBPs hold a central position in IGF ligand-receptor interactions through influences on both the bioavailability and distribution of IGFs in the extracellular environment. Insulin like growth factor binding protein 3 (IGFBP3) can modulate the mitogenic and metabolic effects of the insulin like growth factors (IGFs). Insulin like growth factor binding protein 3 (IGFBP3) is expressed in multiple tissues. The highest expression level is found in the non paranchymal cells of the liver. The expression levels are higher during extrauterine life and peak during puberty. Insulin like growth factors (IGFs) and IGF binding proteins (IGFBPs) play important roles in cell growth and differentiation. IGFBP3 is one of the factors in serum that is responsible for high serum induced apoptosis in PC3 cells, a prostate cancer cell line. IGFBP3 is important in controlling glucose homeostasis with increased urinary levels in type I diabetes with persistent microalbuminuria.