Angiopoietin-1 (Ang-1) is a secreted glycoprotein that plays a critical role in the development and maintenance of the vascular system. It signals through the receptor tyrosine kinase Tie-2 and binds a variety of integrins and the extracellular matrix. Angiopoietin-1 induces the development and branching of blood vessels, promotes vascular endothelial cell motility during angiogenesis, and enhances vascular integrity. It can suppress several VEGF-induced effects on the vasculature. Angiopoietin-1 can protect against pulmonary arterial hypertension, reduce the extent of fibrosis and remodeling in infarcted diabetic myocardium, and enhance tumor progression and metastasis.