The PDE5A Assay Kit is designed for identification of PDE5A inhibitors using fluorescence polarization. The assay is based on the binding of a fluorescent nucleotide monophosphate generated by PDE5A to the binding agent. The key to the PDE5A Assay Kit is the specific binding agent. Using this kit, only two simple steps on a microtiter plate are required for PDE5A reactions. First, the fluorescently labeled cGMP is incubated with PDE5A for 1 hour. Second, the binding agent is added to the reaction mix to produce a change in fluorescent polarization that can then be measured using a fluorescence reader equipped for the measurement of fluorescence polarization.