Subcutaneous transplantation of skin results in the formation of epidermal cysts which ultimately

the formation of epidermal cysts which ultimately undergo destruction (3, 4). Application of @2Omethyicholanthrene to the epidermis of young adult mice previous to transplantation stimulated epithelial growth in cutaneous and subcutaneous grafts made from skin thus treated. These grafts were likewise destroyed, unless the epithelium had, in the course of painting, acquired neoplastic properties (8) . Neoplastic growth was, however, readily obtained if skin of mouse embryos was exposed to carcinogens previous to transplanta tion (6, 10, 11). The change in transplantability following stimulation by a carcinogen seems of in terest in view of the role attributed to the seba ceous glands in epidermal carcinogenesis (6, 9—U2). We therefore decided to study the transplanta hility of neonatal skin at various stages of develop inent and following treatment with a carcinogen.