IGF-1 (Insulin-Like Growth Factor 1) is a member of the IGF family with potent mitogenic and metabolic effects. IGF-1 is produced mainly in the liver and is secreted into the blood, where is circulates bound to one of six IGF-binding proteins (IGFBPs). Of these proteins, IGFBP-3 is present at the highest level in adults, and is responsible for carrying IGF-1 to target tissues and prolonging it’s half-life in circulation. In contrast, IGFBP-1 is the most important negative regulator of IGF-1. Along with circulating IGF-1, lower levels of the protein are also produced in most tissues, where it functions in a paracrine or autocrine manner. IGF-1 plays an important role in growth and metabolism, and shares many overlapping functions with insulin and IGF-2. Human IGF-1 exhibits 70% and 94% sequence homology with human IGF-2 and mouse IGF-1, respectively, and displays cross-species activity.