Peroxide Block is used in immunohistochemical staining for blocking endogenous peroxidase in the tissue. This step is necessary in immunohistochemistry when using HRP enzyme-labeled secondary antibody. If this step is skipped, endogenous peroxidase can cause precipitation of DAB chromogen resulting in strong background staining or a false positive result. It is used with samples fixed with formalin or glyoxal and embedded in paraffin. Peroxide Block is a stabilized reagent that does not require mixing or dilution.