RORa, b and g are nuclear receptors (NRs) belonging to the retinoic acid receptor-related orphan receptor family. By identifying selective inhibitors against ROR g we hope to be able to prevent development of Th17 cells, cells that are implicated in several human autoimmune diseases. RORa is expressed in the whole body and plays an essential role in regulation of circadian rhythm. The key question for these compounds is how much activity they exhibit towards the RORa receptor. We set out to develop a ROR? binding assay using multiple approaches such as surface plasmon resonance (SPR), nuclear magnetic resonance (NMR) spectroscopy and radioligand binding. SPR, NMR and radioligand binding approaches were unsuccessful. We are confident that we have a functional protein demonstrated through binding to co-activator peptides and have subsequently developed a ligand dependent co-activator recruitment assay for RORa utilizing a PGC-1a co-regulator peptide capable of identifying both agonists, inverse agonists and antagonists. Here we present assay development data to illustrate the challenges in the establishment of a biochemical assay for RORa.