Abstract It has been shown that when a direct binding assay, such as equilibrium dialysis, is used to measure antibody site concentration an underestimate of the concentration of low affinity antibodies may occur in the presence of small amounts of high affinity antibody. Removal of high affinity antibody by use of a solid immunoadsorbent permits detection of more low affinity antibody than was detected by assaying the original serum sample. It appears likely that immune sera frequently contain considerably larger concentrations of low affinity antibodies than can be detected by conventional assay methods.