Abstract: A method for assaying for a ligand analyte which is a member of a specific binding pair ("sbp member") consisting of ligand and its complementary receptor is disclosed. The ligand analyte has a binding site in common with an interfering substance present in a sample suspected of containing the analyte. The interfering substance has at least two binding sites. The method comprises combining in an assay medium without intervening separation (1) the sample, (2) a blocking receptor which does not bind to the ligand and does bind to the interfering substance, thereby blocking the binding of a common receptor to the interfering substance, and (3) a common receptor which binds to the common binding site. Any additional members of a signal producing system capable of producing a detectable signal in relation to the amount of analyte in the sample are added to the assay medium. Next, the assay medium is examined for the presence of a detectable signal.