FGF acidic, also known as FGF-1, ECGF, and HBGF-1, is a secreted mitogen that stimulates the proliferation of all cells of mesodermal origin and many cells of neuroectodermal, ectodermal, and endodermal origin. It plays a number of roles in development, regeneration, and angiogenesis. FGF acidic is released extracellularly as a disulfide-linked homodimer and is stored in complex with extracellular heparan sulfate. The association of FGF acidic with heparan sulfate is a prerequisite for its subsequent interaction with FGF receptors. Internalized FGF acidic can translocate to the cytosol and to the nucleus. Intracellular FGF acidic functions as a survival factor by inhibiting p53 activity and proapoptotic signaling.