The Estrogen Receptor-βCompetitor Assay, Red kit assesses the affinity of test compounds to ERβ(54kDa). ERβis added to a fluorescent estrogen ligand to form an ER/Fluormone™EL Red complex. This complex is then added to individual test compounds in multiwall plates. To determine relative affinity, the assay measures fluorescence polarization. Competing test compounds will displace the Fluormone™EL Red ligand from ERβpermitting it to tumble rapidly and result in low polarization value. By using longer wavelength excitation (530nm) than used for the ER Competitor Assay, Green kits the problem of intrinsic fluorescence found in some test compounds is greatly reduced.