Pepsin is used for proteolytic digestion of formalin-fixed paraffin-embedded (FFPE) tissue sections prior to application of antibodies. In immunohistochemistry (IHC), most commonly used fixatives such as formalin mask tissue antigens (cellular, membrane, and nuclear) by their intrinsic crosslinking. This masking results in poor or no staining in IHC. Pepsin digestion of FFPE tissue sections improves accessibility of antibodies to tissue antigens. Ready to use pepsin reagent, antigen retriever has been used for antigen unmasking in immunohistochemistry.