THE ROLE of the liver in the production of the various coagulation factors has not been fully elucidated. That factors II (prothrombin), VII, IX (plasma thromboplastin component), and X (Stuart factor) are synthesized in the liver seems quite clear. These four factors are vitamin-K dependent, are commonly deficient in severe liver disease, and are rapidly decreased following experimental liver damage or hepatectomy. In vitro synthesis of factors II and VII by rat liver slices was demonstrated by Pool and Robinson.1 Barnhart and Anderson2 have localized factor II in the liver parenchymal cells by fluorescent antibody technique. Although patients with severe liver disease rarely show hypofibrinogenemia, much evidence suggests that the liver must be one, if not the only, site of factor I (fibrinogen) synthesis. Fibrinogen disappears rapidly after hepatectomy,3 it has been localized in the microsomal and soluble fractions of the liver parenchymal cells,4 and its in vitro synthesis