Previous investigations have focused on the skin manifestations, histopathology, and pedigree of patients with Dowling-Degos disease (DDD). Little is known about its immunohistochemical staining, and electron microscopy. Our purpose was to study the immunohistochemistry and electron microscopy of lesions from patients with DDD. A biopsy specimen revealed elongated epidermal rete ridges with basilar hyperpigmentation in a filiform pattern. All pigmented cells in the basal layer were recognized by Anti-PEP-1, anti-PEP-2, HMB-45 and NKI/beteb antibodies. The melanocytes were localized in the basal layer and accounted for 10% of the total keratinocytes. There were supranuclear "caps" of brown granules within most basal kerotinocytes in the hyperpigmentation area. The melanocytes contained many mitochondria, Golgi apparati, and regular melanosomes in all stages of maturation in their cytoplasms; melanosome-laden dendrites were readily detected by transmission electron microscepe. Melanosomes, mainly of stages III and IV, were present within keratinocytes, distributed either as scattered patterns or forming "caps" over the nucleus.