To clarify the histopathogenesis of Pinkus tumor (fibroepithelial basal cell carcinoma, FEBCC), we have studied cytokeratin (CK) expression in FEBCC using ten different anti-keratin antibodies against CK 1, 7, 8, 10, 14, 15, 16, 17, 18 and 19. Tumor nests consisted of two epithelial components: duct-like structures and basaloid cells of anastomosing strands. In duct-like structure, CK 1, 10, 14, 16, 17 and 19 were detected. CK expression of duct-like structure showed the hyperproliferative state of eccrine intraepidermal ducts. In basaloid cells of anastomosing strands, CK 14 and 17 were detectable. These results suggested that duct-like structure originates from the intraepidermal duct and proliferates to spread in the dermis.