The PDE1A Assay Kit is designed for identification of PDE1A inhibitors using fluorescence polarization. The assay is based on the binding of a fluorescent nucleotide monophosphate generated by PDE1A1 to the binding agent. The key to the PDE1A Assay Kit is the specific binding agent. Using this kit, only two simple steps on a microtiter plate are required for PDE1A reactions. First, the fluorescently labeled cAMP is incubated with a sample containing PDE1A1 for 1 hour. Second, a binding agent is added to the reaction mix to produce a change in fluorescent polarization. The FP signal is measured using a fluorescent microplate reader capable of measuring fluorescence polarization.