PAP pen provides a thin, film like water repellant barrier when a circle is drawn around the specimen on the glass slide. This barrier creates the proper surface tension to hold antibody solution within the target area on the slide. This avoids the repeated wipeout around the specimen during the staining procedure. Since the reagent is guarded by the hydrophobic circle around the tissue, it minimizes the undesirable dilution of the reagents with the wash buffer. This pen can be used for PAP, ABC, immunofluorescence method, frozen sections and in situ hybridization procedures. Two specimens separated by two circles can be applied to the same slide.