Studies with heat-inactivated MS-2 serum have indicated that active immunization against hepatitis B infection can be achieved even though the virus has not been cultivated in tissue culture. The development of new biophysical, biochemical and immunological techniques has increased knowledge of the hepatitis B virus and its associated antigens. In the wake of these recent developments the accumulating evidence indicates that active immunization could be achieved by the use of purified hepatitis B surface antigen or by one of its polypeptides or glycolipids.