Summary: Significant amounts of superoxide dismutase (SOD) in cellular and extracellular environments are crucial for the prevention of diseases linked to oxidative stress. Mutations in SOD account for approximately 20% of familial amyotrophic lateral sclerosis (ALS) cases. SOD also appears to be important in the prevention of other neurodegenerative disorders such as Alzheimer's, Parkinson's, and Huntington's Diseases. The reaction catalyzed by SOD is extremely fast, having a turnover of 2 x 10^6 M-1sec-1 and the presence of sufficient amounts of the enzyme in cells and tissues typically keeps the concentration of superoxide very low. Quantification of SOD activity is therefore essential in order to fully characterize the antioxidant capabilities of a biological system. The Cayman Chemical SOD Assay kit is a fast and reliable assay for the measurement of SOD activity from plasma, serum, tissue homogenates, and cell lysates. SOD activity is assessed by measuring the dismutation of superoxide radicals generated by xanthine oxidase and hypoxanthine in a convenient 96 well format. A key feature of the kit is the inclusion of a quality-controlled SOD standard. The standard curve generated using this enzyme provides a means to accurately quantify the activity of all three types of SOD (Cu\/Zn-, Mn-, and Fe-SOD). Each kit contains sufficient reagents to assay 41 samples in duplicate and includes assay buffer, sample buffer, radical detector, SOD (standard), xanthine oxidase, a 96 well plate, and complete instructions.