The so-called "epidermal sweat duct unit"1 has long been a subject of controversy. The intraepidermal portion of the eccrine sweat duct has been considered by some to have a specialized epithelium, while others have felt that this portion of the duct is lined by typical epidermal cells. Physiologically, a final clarification of this matter would be of great importance. Charles,2 in an electron microscopic study of the eccrine sweat gland, mentioned the epidermal sweat duct. He did not depict the orifice in the stratum corneum, but in summary, stated that "as the duct ascends to the epidermis the large lumen first becomes surrounded by a dark, papillate cuticle, and then becomes completely occluded, the only channel left for the passage of sweat being between closely adpressed papillae. Within the epidermis the cuticle appears to keratinize and an unspecialized pore is formed." A study was undertaken, using the electron