Seven cases of sweat-gland carcinomas showing eccrine ductal differentiation (ductal carcinomas) are presented. The tumors had a variable histological appearance, but were basically characterized by the following histological elements: (a) tubular structures, sometimes cystic or having a "tadpole" appearance; (b) solid islands of squamous, basaloid, or clear cells; (c) periodic acid-Schiff-positive endoluminal and/or intracellular material; and (d) infiltrating growth. Immunocytochemically, tumor cells were positive for keratin and negative for actin. Endoluminal material contained carcinoembryonic antigen in five of seven cases. Although it is not yet clear whether carcinomas exhibiting eccrine ductal differentiation may represent a specific histotype or a group encompassing several distinct clinicopathological entities, the histological analysis of the cases suggested that the wide spectrum of their histological appearances may be due to variable grades of differentiation.