The Estrogen Receptor-βCompetitor Assay, Green kit assesses the affinity of test compounds to ERβ. ER is added to a fluorescent estrogen ligand to form an ER/Fluormone™ES2 complex. This complex is added to individual test compounds in multiwell plates. To determine relative affinity, the assay measures fluorescence polarization. Competing test compounds will displace the Fluormone™ES2 ligand from ERβpermitting it to tumble rapidly and result in low polarization value. A shift in the fluorescence polarization value in the presence of test compounds is used to determine relative affinity of test compounds for ERβ.