Polyclonal antisera from immunized hosts are lipid extracted to improve clarity, salt fractionated, dialyzed against phosphate buffered saline containing sodium azide and freeze-dried. Antisera against whole serums are obtained by immunizing host animals with whole serum. Antisera against whole IgG molecules [i.e. Anti-IgG (H+L)] are recommended for bridging PAP to primary antibodies.-Based on immunoelectrophoresis, the antibody reacts with the Fc portion of rabbit IgG heavy chain but not with the Fab portion of rabbit immunoglobulins. No antibody was detected against non-immunoglobulin serum proteins. The antibody may cross-react with immunoglobulins from other species.