Two Step HRP Detection System is a kit containing 5 reagents, and it is used for visualization procedure of immunohistochemical staining of samples fixed with formalin or glyoxal and embedded in paraffin blocks. Peroxide Block is used for blocking endogenous peroxidases, a procedure necessary for eliminating background staining and false positive results. The polymerized secondary antibody technology, which is conjugated with peroxidase, enables blocking endogenous biotin and its background signal, and it consists of two components. DAB Concentrate / DAB Substrate consists of two components – DAB chromogen concentrate and DAB substrate. With the presence of peroxidase enzyme conjugated to the secondary antibody, at the location of the antigen DAB forms a brown precipitate that is not soluble in alcohol and xylene. Two Step HRP Detection System is efficient with mouse and rabbit primary antibodies.