Aryl Hydrocarbon Receptor (AhR), also known as bHLHE76, is a 110 kDa member of the bHLH/PAS transcription factor family. It is widely expressed (breast, lung, liver), and serves many functions. It is a ligand-activated transcription factor best known for its role in sensing xenobiotics and regulating the expression of genes involved in xenobiotic metabolism, including drug transporters and drug metabolizing enzymes. Heat Shock Protein 90kDa Alpha A1 (HSP90aA1) has been identified as an interactor of AhR, thus a functional binding ELISA assay was conducted to detect the interaction of recombinant human AhR and recombinant human HSP90aA1. Briefly, AhR were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100 µl were then transferred to HSP90aA1-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-AhR pAb, then aspirated and washed 3 times. After incubation with HRP labelled secondary antibody, wells were aspirated and washed 5 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50 µL stop solution to the wells and read at 450 nm immediately. The binding activity of AhR and HSP90aA1 was shown in Figure 1, and this effect was in a dose dependent manner, the EC50 for this effect is 0.09 ug/mL.