Liquid Blocker (Pap Pen) makes a water repellent circle which avoids the procedure to wipe-out around the section as used to at every staining of antiserum. Since serum is guarded by the Liquid Blocker circle, it is assured of getting successful work-out in staining. Circle made by Liquid Blocker is removable by xylene. Since it is not influenced by water-soluble mounting media, there is no interruption for the microscopic observation. This water repllent Liquid Blocker is also applicable to the microwave staining, in situ hibridization, etc.