The present invention provides a method of testing the ability of a test compound to bind to and optionally modulate the activity of a protein of the JMJD2 subfamily of Jumonji proteins. The method comprises incubating a test compound with a protein of the JMJD2 subfamily of Jumonji proteins, a co-factor of said protein and, optionally, a substrate for demethylation. The method of the invention can be used for screening large numbers of compounds to identify a group of compounds that are candidate compounds for clinical use for treatment of certain cancers especially prostate cancers. Other compounds that do not have activity in the screening assays can be eliminated from further consideration as candidate compounds. The method of the invention therefore has utility in the pharmaceutical industry.