The study by B. S. Blumberg on the polymorphism of human antigens led to the discovery in 1964 of the viral cause of hepatitis, a disease of the liver in humans (Blumberg 1977). The experimental approach used by Blumberg was to search for antibodies to antigens in the peripheral blood of patients who had received a large number of blood transfusions. He looked for antibodies produced against unique antigens in the blood of the donors that would differ from the blood group antigens, which are always matched with that of the recipient. In this study, sera from individuals all over the world—from the Eskimos in the north of Alaska to the aborigines in Australia—were tested. A hemophiliac in New York who had received many blood transfusions was found to have antibodies in his serum that gave a precipitation line in the Ouchtherlony test with an antigen present in the serum of an Australian aborigine. For this reason, the antigen was designated Australia (Au) antigen. Studies of sera received from hospitalized children with Down’s syndrome (mongoloidism) revealed that one of the children who initially lacked antibodies to Au antigen subsequently developed such antibodies after being ill with hepatitis. Thus a correlation between active hepatitis and antibodies to Au antigen was made. In 1967, the chief technician in Blumberg’s laboratory, while working on the purification of the antigen, developed hepatitis. Antibodies in her serum gave a precipitation like with Au antigen, and for the first time hepatitis was diagnosed with the help of an antigen. Shortly thereafter, it was concluded that transfusion of blood containing Au antigen results in infection of the patient with hepatitis virus. Since 1969, every blood donation used in the USA for transfusion must be tested for Au antigen, and the positive blood samples are discarded. The Au antigen, also called the hepatitis-associated antigen (HAA) or SH-antigen, was subsequently found to be the surface antigen, HBsAg, of hepatitis B virus (HBV).