PURPOSE. The authors investigated the phenotypic characteristics of basally located "transitional cells" in peripheral superior cornea, characterized previously by their coexpression of cytokeratin 19 and vimentin and their negativity for AE5. METHODS. Twenty adult human corneas were studied, using in situ immunohistochemical techniques and a panel of specific monoclonal antibodies against various surface and cytoplasmic molecules. RESULTS. The transitional cells shared staining characteristics with limbal basal cells in their expression of alpha 6 beta 4-integrin, metallothionein, AE1, and transferrin receptor. CONCLUSIONS. These "transitional" epithelial cells exhibit a unique phenotype differing from that of the surrounding basal epithelial cells in the peripheral cornea but analogous to that of limbal basal cells. These findings further corroborate the hypothesis that, at least from an immunohistochemical point of view, transitional cells in the superior peripheral cornea exhibit stem cell characteristics.