Cytokeratin 15 (CK15) is involved in the development of stratified epithelia from one-layered polar epithelia and continues to be expressed in several adult epithelial tissues. It labels the basal keratinocytes of stratified tissues, including the fetal epidermis and fetal nail. Although CK15 in normal hair follicles was virtually absent from hair bulbs, it was expressed by a subset of keratinocytes in the outer root sheath. In human conjunctival epithelium, strong expression of CK15 was observed in basal cells, whereas Cytokeratin 19 was expressed in both basal and suprabasal layers. CK15 may be used to differentiate primary from metastatic skin cancer. It may be a useful stem cell marker for hair follicle and breast epithelium.