Protein Block has been developed for use in immunohistochemical assays. It is applied to the tissue sample prior to the application of the primary antibody to reduce nonspecific background staining while simultaneously reducing the handling of animal serums in the laboratory. The need to match species with the secondary antibody was eliminated with the use of this product. Protein Block comes ready-to-use and requires no mixing or diluting. Protein Block may be used for other immunoassay upon optimization and verification by the end user.