The histochemical and electron microscopic findings in seven cases of dermal duct tumor are described. All seven of the patients were elderly, and five were women. The tumors were small flesh-colored or red papules located most often on the head and neck region. Intense phosphorylase and moderate respiratory enzymes characterized the histochemical reaction of the tumors. The following three types of tumor cells were recognized ultrastructurally: clear, dark, and luminal. The tumor was principally composed of clear cell proliferation around a regular ductal lumen. In addition, melanocytes, Langerhans' cells, and lymphocytes were occasionally seen within the tumor masses. An intact basal lamina and few hemidesmosomes with no detectable actin-like microfilaments were the features of the tumor-stroma interface. Our study results showed that the dermal duct tumor is a benign tumor with eccrine dermal ductal differentiation.