Jumonji Domain Containing 2D (JMJD2D) is a Jumonji C (JmjC) histone demethylase that catalyzes the demethylation of di- and trimethylated lysine 9 of histone H3. Cayman's JMJD2D Inhibitor Screening Assay Kit provides a convenient fluorescence-based method for screening JMJD2D inhibitors. The assay is based on the multistep reaction in which JMJD2D first produces formaldehyde during the demethylation of the trimethylated peptide substrate, histone H3 trimethyl lys9, with the concomitant oxidation/decarboxylation of 2-oxoglutarate. The detection reaction involves the cyclization between formaldehyde and acetoacetanilide in the presence of ammonia. The resulting fluorescent product is analyzed using an excitation wavelength between 365-375 nm and an emission wavelength between 465-475 nm.