Cyclooxygenase (COX, also called Prostaglandin H Synthase or PGHS) is a bifunctional enzyme exhibiting both COX and peroxidase activities. The COX component converts arachidonic acid to a hydroperoxy endoperoxide (PGG2), and the peroxidase component reduces the endoperoxide to the corresponding alcohol (PGH2), the precursor of PGs, thromboxanes, and prostacyclins. It is now well established that there are two distinct isoforms of COX, COX-1 and COX-2. Cayman"s COX Fluorescent Inhibitor Screening Assay provides a convenient fluorescence-based method for screening ovine COX-1 and human recombinant COX-2 for isozyme-specific inhibitors. The assay utilizes the peroxidase component of COXs. In this assay, the reaction between PGG2 and ADHP (10-acetyl-3,7-dihydroxyphenoxazine) produces the highly fluorescent compound resorufin. Resorufin fluorescence can be analyzed with an excitation wavelength of 530-540 nm and an emission wavelength of 585-595 nm.