Noun | 1. | immunoassay - identification of a substance (especially a protein) by its action as an antigen; "PSA in the blood can be measured with an immunochemical assay" bioassay, bio-assay - appraisal of the biological activity of a substance by testing its effect on an organism and comparing the result with some agreed standard radioimmunoassay - immunoassay of a substance that has been radioactively labeled |