Cayman's Myeloperoxidase Chlorination Fluorometric Assay provides a convenient fluorescence-based method for detecting the MPO chlorination activity in both crude cell lysates and purified enzyme preparations. The assay utilizes the non-fluorescent 2-[6-(4-aminophenoxy)-3-oxo-3H-xanthen-9-yl]-benzoic acid (APF), which is selectively cleaved by hypochlorite (-OCl) to yield the highly fluorescent compound fluorescein.{11242} Fluorescein fluorescence is analyzed with an excitation wavelength of 480-495 nm and an emission wavelength of 515-525 nm. The kit includes a MPO-specific inhibitor for distinguishing MPO activity from MPO-independent fluorescence.