The cytokeratin expression of Merkel cells in fetal rat skin was studied by light- and electron microscopy. Employing a pre-embedding staining method, 2 monoclonal anti-keratin antibodies (RCK-102, MA-902) were shown to stain Merkel cells specifically. Neighbouring keratinocytes were unstained. The staining reaction seems to be based on the expression of 52.5 kD cytokeratin.