||Prostaglandin D2 (PGD2) is synthesized by hematopoietic-type PGD-synthase (H-PGDS) in mast cells and is released in large quantities during allergic and asthmatic anaphylaxis. H-PGDS is therefore a key target for development of selective, potent inhibitors for therapeutic use against these diseases. The H-PGDS FP-Based Inhibitor Screening Assay Kit - Green provides a rapid, accurate assay for screening H-PGDS inhibitors. In this assay, a H-PGDS inhibitor-fluorescein conjugate serves as a specific fluorescent probe for the enzyme. Displacement of the probe by any unlabeled H-PGDS inhibitor leads to a decrease in the fluorescence polarization (FP) state of the probe, providing a direct signal for binding of the inhibitor to the active site of the enzyme. This assay is robust (Z" of 0.75) and eliminates the need for the traditional multistep assay that requires the use of highly unstable PGH2. The assay has been validated using several known inhibitors of H-PGDS with IC50 values ranging from nanomolar to millimolar concentrations.