Insulin-like growth factor-binding protein 4 (IGF-BP-4), also known as IBP-4, is a secreted glycoprotein belonging to the IGFBP family. IGF-BP-4 is produced by osteoblasts, epidermis, ovarian follicles and other tissues. It binds both insulin-like growth factor (IGF) I and II, and it circulates in the plasma in both glycosylated and non-glycosylated forms. IGF-BP-4 prolongs the half-life of the IGFs and has been shown to inhibit or stimulate the growth-promoting effects of the IGFs. Pregnancy Associated Plasma Protein A (PAPP-A) proteolytically cleaves IGF-BP-4 and reduces its affinity to bind IGFs, and thus serves as an important regulator of IGF-BP-4 function.