Kit contains the reagents necessary to perform a competition assay for identification of Androgen receptor (AR) binding compounds. The kit uses the rat AR ligand-binding domain tagged with His and GST [AR-LBD(His-GST)]. AR-LBD(His-GST) is added to a fluorescently-tagged androgen ligand (Fluormone™AL Green) in the presence of competitor test compounds in microwell plates. The presence of effective competitors prevents the formation of a AL Green/ AR-LBD(His-GST) complex resulting in a decrease of the polarization value due to ligand displacement caused by a competitor. The shift in polarization value in the presence of test compounds is used to determine relative affinity of test compounds for AR-LBD(His-GST).