Vascular endothelial growth factor (VEGF)/vascular permeability factor is the prototype for a growing family of dimeric growth factors, which exert their effects on vascular and lymphatic endothelial cells, as well as on a wide range of other cell types. Gene targeting shows that most, if not all, of the factors and receptors in this family serve critical functions during vascular development or in adult physiological and pathological angiogenesis. Growing tumours produce VEGF, and many different strategies for inhibiting tumour growth by inhibiting VEGF production are being tested in clinical trials at present. This review focuses on the signal transduction properties of VEGF receptor-1 and VEGF receptor-2.