The PAP Pen is a useful pen-like tool for immunohistochemical staining methods. It is designed to prevent the waste of valuable reagents by forming a water-repellent barrier around the specimen. This barrier creates the proper surface tension to hold an antibody solution or detection reagents within the target area on the slide. The surface tension provided by the PAP Pen circle ensures that only the amount of antibody solution needed for sufficient reaction will be applied. Since over-flooding of the slide is eliminated, wiping of excess fluid around the specimen can be avoided. The PAP Pen can be used for immunostaining of paraffin sections, frozen sections, and for fluorescent antibody methods. The PAP Pen contains a special formulation, which is water repellent. It can be removed, if desired, with xylene or xylene substitutes after the staining procedure is completed.