This assay employs the quantitative sandwich enzyme immunoassay technique. A monoclonal antibody specific for IL-13 has been pre-coated onto a microplate. Standards and samples are pipetted into the wells and any IL-13 present is bound by the immobilized antibody. After washing away any unbound substances, an enzyme-linked polyclonal antibody specific for IL-13 is added to the wells. Following a wash to remove any unbound antibody-enzyme reagent, a substrate solution is added to the wells and color develops in proportion to the amount of IL-13 bound in the initial step. The color development is stopped and the intensity of the color is measured.