The "blood business" concerns blood collection, transfusion, and the manufacture of blood products, like gamma globulin, blood-clotting proteins, or albumin, that are steady products taken from blood plasma. Research in hematology and immunology and the official organization of blood transfusions contributed to the emergence of a "blood business" in France after World War II. Physicians, scientists, but also manufacturers and high-ranking civil servants set up and organized this business, under the control of the law of July 21, 1952, and the decrees of 1954 that prohibited any profit from the blood business. Nevertheless, for about three decades, a "quite public" organization and some enterprises manufactured blood products. These two circles met and collaborated with different aims: enforcement of the law on blood products, research projects, and assessment of the products. First, we will analyze the organization of blood transfusions after World War II at the national level and at a local level, in Lyon. Then we shall examine how the responsibilities were shared among scientists, physicians, and industrialists for the organization of manufacturing and the development of some innovations. Last, the crisis in the 1970s and 1980s reveals competition between networks, the use of lobbying, and also how the "quite public" organization, the CNTS, failed to imitate the enterprises in their blood business strategies.