Summary We examined the presence and the distribution of epithelial membrane antigen (EMA), carcinoembryonic antigen (CEA), and keratin in 4 cases (6 specimens) of mammary Paget's disease and 9 cases (18 specimens) of extramammary Paget's disease utilizing immunoperoxidase technique. Paget's cells in 23 out of 24 specimens were demonstrable for EMA. Positive staining was observed for CEA in every specimen. Among the 24 specimens, 16 showed positivity for keratin. In addition, CEA was positive in Paget's cells and the staining for CEA was stronger than that of EMA and keratin. On the other hand, some Paget's cells were negative for EMA of keratin although other positive cells were observed in the same sections. This findings indicates that Paget's cells might express CEA and/or EMA and/or keratin depending on their differentiation. EMA is present in most organs showing glandular differentiation, and anti-keratin antibody used in this study recognizes not only keratinocytes but glandular cells. Thus, our study suggests Paget's cells are of glandular origin.