Catalase is a ubiquitously expressed antioxidant enzyme that can be found in most of the living organisms. It catalyzes the decomposition of hydrogen peroxide (H₂O₂) to water and oxygen. The Catalase Activity Colorimetric/Fluorometric Assay Kit offers an easy and sensitive way for measuring Catalase activity and detects high pico-unit of catalase in biological samples. In this assay, catalase first reacts with H₂O₂ to produce water and oxygen, the unconverted H₂O₂ reacts with OxiRed probe to generate a product that can be detected colorimetrically at 570 nm or fluorometrically at Ex/Em = 535/587 nm. Catalase activity is reversely proportional to the signal.