Vascular endothelial growth factor (VEGF or VEGF-A) is a potent mediator of both angiogenesis and vasculogenesis in the fetus and adult. It is a member of the PDGF family. Humans express alternately spliced isoforms of 121, 145, 165, 183, 189, and 206 amino acids (aa) in length. VEGF165 appears to be the most abundant and potent isoform, contains basic heparin-binding regions and is not freely diffusible. VEGF binds the type I transmembrane receptor tyrosine kinases VEGF R1 (also called Flt-1) and VEGF R2 (Flk-1/KDR) on endothelial cells. VEGF165 binds the semaphorin receptor, Neuropilin-1 and promotes complex formation with VEGF R2. VEGF is required during embryogenesis to regulate the proliferation, migration, and survival of endothelial cells. In adults, VEGF functions mainly in wound healing and the female reproductive cycle. Pathologically, it is involved in tumor angiogenesis and vascular leakage. Circulating VEGF levels correlate with disease activity in autoimmune diseases such as rheumatoid arthritis, multiple sclerosis and systemic lupus erythematosus.