Immunohistochemistry is a suitable method for the detection of proteins from the Claudin family and several antibodies are commercially available for the detection of Claudin congeners. Immunodetection of Caludin-4 in the paraffin-embedded specimens might be a useful tool for studying the role of these proteins in the cyclic transformation of the endometrium and its role in the endometrial receptivity; furthermore, other components of the junctional zone involved in the transformational process of the endometrium can be detected by means of immunohistochemistry/immunofluorescence with several polyclonal or monoclonal antibodies. The aim of this chapter is to comprehensively overview the materials and methods to perform the endometrial biopsy and to detect Claudin-4 in paraffin-embedded samples of endometrium. Additionally, the interpretation of the results is addressed.