Examination of 340 nipples from cancerous breasts revealed histologically benign clear-cell infiltrates in 31. Nipple-duct cancer coexisted in but a single instance. These findings suggested that the epidermal infiltrates were of nonneoplastic nature and, consequently, were to be distinguished from the infiltrate of Paget's disease. Examination of 190 nipples removed from 101 autopsy subjects disclosed, within 23, epidermal infiltrates morphologically similar to those present within the surgical specimens. Nipple-duct cancer was not encountered. Within the clear-cell aggregates, tubular structures resembling mammary ductules were observed. It is believed that the cellular complexes referred to represent nonneoplastic mammary elements within the nipple epidermis. These complexes may possibly provide an anatomical basis for the development of Paget's disease as a primary intra-epidermal malignancy. Distinction from the cancerous nipple infiltrate of Paget's disease is of both histogenetic and practical importance.