A simple procedure to use whole serum as a source of either IgG- or IgM-specific antibody.

Absorption of rabbit antiserum to Forssman antigen with immobilized staphylococcal Protein A or concanavalin A selectively removed IgG or IgM antibodies, respectively. This absorption procedure was more rapid than ion exchange chromatography on DEAE cellulose or molecular sieving on Sephadex G-200 and gave a better yield of functionally purer antibody. This absorption method gave antiserum suitable for the preparation of either IgM or IgG sensitized sheep erythrocytes and should be of value for the large-scale preparation of indicator cells required for the study of complement action and for detection of specific receptors on cell surfaces.