Formalin fixation forms protein cross-links that can mask the antigenic sites in tissue specimens, thereby creating weak or false negative staining for immunohistochemical detection of certain proteins. There are currently several antigen retrieval methods commonly used and the protocols below only intended as a general guide. Polysciences, Inc. provides AR buffer kits, that include rinses and pH adjustment reagents for the 20X concentration kit. These kits are recommended for formalin fixed paraffin embedded tissues.