The sheep placenta is an often used model in placental research. Uterine epithelium and trophoblast of this synepitheliochorial placenta form a complex, intensely interdigitating epithelial barrier separating maternal and fetal organisms. The close topographical relation and additionally the presence of hybrid syncytia formed by focal fusion of both epithelia hamper identification of the various cellular constituents. Therefore we aimed to find a specific immunohistochemical marker differentiating between the fetomaternal syncytial plaques and trophoblast. A monoclonal antibody directed against type II cytokeratins strongly stained unicellular trophoblast. The syncytial plaques were only weakly stained while binucleate trophoblast remained unstained. This antibody proved to be a useful tool for easy histological orientation in the sheep placenta. In combination with other antibodies in double immunohistochemistry it facilitates exact localization of antigens.