Angiotensinogen (AGT), also known as SerpinA8, is a member of the serine protease inhibitor family. AGT is an α-2-globulin produced and released into the circulation by the liver. AGT is an essential component of the renin-angiotensin system and is an effective blood pressure regulator. AGT can be cleaved into three chains: angiotensin-1, angiotensin-2, and angiotensin-3. The absence of AGT is associated with primary hypertension and renal tubular dysgenesis. Some serine protease inhibitors, such as antithrombin, maspin, pigment epithelium-derived factor, and kallistatin, have recently been shown to have antiangiogenic activity, indicating a common mechanism for endothelial cell proliferation and migration. AGT and its renin-cleavage products are also angiogenesis inhibitors within the plasma concentration range observed in vitro and in vivo.