HBc Ag is prepared by isolating Dane particles by isopycnic banding of fluid from HBs Ag positive donors, optionally but preferably pelleting the Dane particles, and then removing the surface antigen by contacting the Dane particles with a nonionic surfactant having from about 15 to about 35 oxyethylene units in the presence of a reducing agent such as mercaptoethanol. The isolated core antigen is used as a diagnostic and immunologic agent.
