Angiostatin is a proteolytic fragment of plasminogen constituting kringles 1 - 4. It is a potent angiogenesis inhibitor and the inhibition of angiogenesis by angiostatin is directly related to inhibiting the proliferation of endothelial cells. Human Angiostatin significantly inhibits bFGF-induced endothelial cell proliferation and migration at concentrations ranging from 300 nM – 1.0 uM.