DNA has been isolated from the cores of Dane particles and is associated with a specific DNA polymerase. Robinson has shown that the DNA is in the form of double stranded rings (22). Jesse Summers, Anna O’Connell and Irving Millman of our Institute have confirmed these findings and provided a model for the molecule which appears to have double and single stranded regions (Fig. 3) (26). Using immunofluorescent and electron microscope studies, hepatitis B core particles have been identified in the nuclei of liver cells of infected patients. HBsAg is found in the cytoplasm. It is thought that assembly of the large particles occurs in the cytoplasm and that large and small particles (surface antigen only) emerge from the cells and eventually find their way to the peripheral blood.