The various patterns of biologic behavior that cells of the epidermal system may assume under normal and pathologic circumstances arc well known. This property is referred to as the pluripotentiality of the epidcrmal cell. The necessary basic factors that determine the specific response of the cpidcrmal cell in each circumstance arc unknown. In a broad sense, the pluripotential capacity of the epidcrmal cell is best revealed by comparing its behavior with that of closely re-lated cpithclial cells, particularly those of the stratified squamous mucosa at the muco-cutanc-ous junctions. The various cpithclial cell lines of the integument and the mucous membranes differ greatly in behavior and morphologic characteristics depending upon their respective locations. One may tentatively conclude that the structural features and functional capacities assumed by the epithclial cell in each location is determined by the environmental milieu in which it finds itself. More specifically, it might be surmised that the determinants arc found in the connective stroma of each location, since this is suggested by evidence such as snbmittcd by Grobstcin (1) and Aucrbach (2) and others who have shown that the development of cpithclial cells in embryonic tissues is influenced differently by environments of mcsenchymc derived from different anatomic locations. However, these experiments were per-formed with embryonic tissue and may pertain only to permanent irreversible changes in cell lines that occur during development, ie differen-tiation. It is clear that differentiated adult cpi-thclial cells can undergo changes in structure and function within limits—for example, under cer-tain conditions cells of piloscbaceous follicles may form epidermis (3), and epidermis in turn may produce new pilosebaccous follicles (4, 5). The in-ference that an influence of connective tissue stroma modulates the behavior and structure of