Summary: The ERR (estrogen related receptor) alpha TR-FRET Coactivator Assay provides a sensitive and robust method for high-throughput screening of potential ERR alpha ligands as inverse agonists (sometimes referred to as antagonists) of coactivator displacement. The kit uses a terbium (Tb)-labeled anti-GST antibody, a fluorescein-labeled coactivator peptide, and an ERR alpha ligand-binding domain (ERR alpha-LBD) that is tagged with glutathione-S-transferase (GST), in a homogeneous mix-and-read assay format.