Anti-hepatitis B immunoglobulin, prepared by a method which involves the initial removal of the fibrinogen fraction, has been reported to lack certain antibodies and fail to detect certain hepatitis B surface antigens when used as a detector reagent in counter-immunoelectrophoresis. The possibility exists that any passive immunity conferred by the immunoglobulin might not protect against these antigens. Anti-hepatitis B immunoglobulin prepared from plasma by a modified technique which omitted the precipitation of the fibrinogen fraction reacted against these antigens in gel precipitin tests. It is suggested that such a method is preferable for the production of anti-hepatitis B surface immunoglobulin.