The PAP PEN is designed to provide a water repellant barrier when a circle is drawn around a specimen such as tissue sections or cells. The barrier of the PAP PEN retains antisera within the defined area and ensures that only the amount of antibody needed for sufficient reaction is used. The PAP PEN stops spreading, reduces waste and divides slides into discreet areas for immunostaining, histology, cytology, cell culture, virology and microbiology. The PAP PEN is effective for immunostaining, PAP method, ABC method, ASD method, enzyme and frozen section methods. The circle is insoluble in acetone and alcohol and can be removed if desired by xylene after the staining procedure. Since water-soluble mounting media does not influence the PAP PEN, there is no interruption in microscopic observation. Properties: 1. Heat resistance up to 120°C. 2. Ready to be used directly on the wet slides. 3. Applicable to microwave staining and in situ hybridization. 4. Circle made by PAP PEN is insoluble in alcohol, acetone. 5. Withstand rehydration and dehydration steps in alcohol. 6. If desired, circle can be removed by xylene after the staining procedure is completed.