Neutrophil elastase is stored within cytoplasmic azurophilic granules in the neutrophil and released upon stimulation by pathogens where it acts either as free protein or is associated with networks of extracellular traps (NET). Together with other proteases released from activated neutrophils, neutrophil elastase plays a critical role in degrading invading pathogens and thus provides the earliest line of defense in the immune system. It is thought to play a critical role in tumor invasion and metastasis as well as other inflammatory conditions. Cayman’s Neutrophil Elastase Activity Assay kit is designed to be used to study compounds regulating elastase release in neutrophils. The kit employs a specific non-fluorescent elastase substrate, (Z-Ala-Ala-Ala-Ala)2Rh110, which is selectively cleaved by elastase to yield the highly fluorescent compound R110, which can be analyzed with an excitation wavelength of 485 nm and emission wavelength of 525 nm. Reagents needed to isolate neutrophils from whole blood are included in the kit, as is PMA, which is known to stimulate elastase release from neutrophils.