We show that a solid-phase immune adsorbent can be prepared from rabbit antiserum by isolating the IgG fraction with the A protein of Staphylococcus aureus associated covalently with a Sepharose matrix. The IgG is then coupled to the matrix using the cross-linking agent dimethylsuberimidate. IgG antibody bound in this fashion is in the proper orientation for combination with antigen because association with protein A occurs via the Fc portion of the IgG molecule, thus leaving the combining site of the molecule free to interact with antigen.