An assay for determining the relative affinity of trace amounts of labeled antibodies.

All assay for the binding efficiency or "relative affinity" of trace amounts of radioactively labeled anti-2,4-dinitrophenyl (DNP) antibodies has been developed. The assay measures the relative ability of the labeled antibodies to combine and precipitate with antigen in the presence of a large amount of unlabeled reference antibody of the same specificity. It has been possible to correlate the relative affinity of the labeled antibodies for dinitrophenylated antigens with the association constants of the reference antibodies for simple univalent DNP ligands.