Abstract.Antibodies to three different samples of hepatitis B antigen‐positive serum were found to be absent from a Cohn fraction II hepatitis B immune globulin preparation, but present in the whole plasma from which the immune globulin was made. Fractions containing the antibodies specific for the three antigen samples were isolated from the plasma by euglobulin precipitation, and the antibodies were characterized as to immunoglobulin class and precipitability in the Cohn fractionation procedure. They appear to be IgG antibodies which, however, were detectable only in Cohn fraction I, while the remainder of the HB specificity present in the original plasma was found, as expected, in fraction I