Porokeratoses: immunohistochemical, light and electron microscopic evaluation. Punch biopsy specimens of 14 patients with porokeratosis of Mibelli (n = 1), disseminated superficial porokeratosis (n = 6), disseminated superficial actinic porokeratosis (n = 4), porokeratosis plantaris, palmaris et disseminata (n = 2), and punctate porokeratosis (n = 1) were obtained for light and electron microscopy for evaluation of possible differences between these clinical variants. Langerhans cells in close contact with early degenerating keratinocytes could be observed in the epidermis. To study the cellular composition of the epidermal inflammatory infiltrate immunohistochemistry was performed. These studies demonstrated that the predominant cell type in these infiltrates are helper T cells, intermingled with Leu-6+ Langerhans cells. Despite the clinical variation and possible different etiologic or triggering mechanisms, the immunohistochemical and morphologic changes in all types of porokeratosis are the same and seem to represent a uniform reaction pattern. 