HEPARIN has been shown to combine with Chargaff's1 lung thromboplastin, which contains phospholipid. It inhibits the formation of intrinsic plasma thromboplastin2, and Douglas3 has shown that it must inhibit blood coagulation at an early stage. Heparin is also known4 to combine specifically with the β-lipoproteins of plasma or serum and to depress the plasma β-lipoprotein concentration when injected in vivo. Christmas factor has been shown to be present in a crude α- and β-globulin fraction of plasma5 and it may contain phospholipid6.