Angiopoeitin-1 (Ang-1) and Antiopoietin-2 (Ang2) are important for development of the endothelium, by regulating tyrosine phosphorylation of the membrane receptor Tie-2/Tek. Ang-1 binding to Tie-2/Tek causes phosphorylation of the receptor. Ang-2 competes for this binding, and thus blocks receptor phosphorylation. Ang-1 has potential fibrinogen-like domain at the carboxy terminus and coiled-coil regions in the amino terminus. Ang-1 is prominently expressed in the myocardium of atrium and ventricle, mesenchymal and smooth muscle cells surrounding most blood vessels, and lung. In the adult, ANG-1 is also expressed in the heart and liver. To our knowledge, this is the first time that an Ang antibody recognises a band above 55 kD. This antibody (and the ang-2 antibody, ab8452) give a band at 75 kD which resembles the original size, because these are soluble highly glycosylated proteins, which should run higher than the calculated molecular weight of 55 kD.