Reactive oxygen species (ROS), such as superoxide and hydrogen peroxide, are constantly produced during metabolic processes in all living species. Superoxide dismutase (SOD), which catalyzes the dismutation of the superoxide anion into hydrogen peroxide and molecular oxygen, is one of the most important antioxidative enzymes. SOD enzymes are classified into three groups: cytosolic Cu/Zn-SOD, mitochondrial Mn-SOD, and extracellular Ec-SOD. The OxiSelect™ Superoxide Dismutase Activity Assay is a fast and reliable kit for the measurement of SOD activity from cell lysate, plasma, serum, tissue homogenates. The assay uses a xanthine/xanthine oxidase (XOD) system to generate superoxide anions. The included chromagen produces a water-soluble formazan dye upon reduction by superoxide anions. Each kit provides sufficient reagents to perform up to 100 assays, including blanks, SOD standards and unknown protein samples.