Many groups of squamoid cells arranged in whorls were found in a case of clear cell hidradenoma. These cells showed positive staining for carcinoembryonic antigen, but S-100 protein was not detected. Electron microscopic examination showed considerable amounts of tonofilaments, but neither keratohyalin granules nor multivesicular dense bodies were present in these cells. These features suggest that the constituting cells of whorls differentiated toward the eccrine ductal cells, in particular the intraepidermal ductal cells.