 Myeloperoxidase, MPO, is an important enzyme found in polymorphonuclear neutrophil cells. It is involved in the production of reactive oxygen and nitrogen species, which are used to combat bacteria and other microorganisms. Inflammation and oxidative stress can cause excessive levels of MPO, leading to various diseases including rheumatoid arthritis, cardiovascular disease, liver disease, diabetes, and cancer. This article was authored by Amjaday Khan, Muhammad El-Salli and Arshad A. Trimani.