T cells play a pathogenic role in many inflammatory and certain malignant skin diseases, including psoriasis, atopic and allergic contact dermatitis, and cutaneous T-cell lymphoma(1-6). Memory T cells that infiltrate the skin express a unique skin-homing receptor called cutaneous lymphocyte-associated antigen (CLA), a carbohydrate epitope that facilitates the targeting of T cells to inflamed skin(1,7,8). CLA is defined by both its reactivity with a unique monoclonal antibody, HECA-452, and its activity as a ligand for E-selectin(2,9-11), but the structure of the protein component of CLA has not previously been defined. Here we report that CLA is an inducible carbohydrate modification of P-selectin glycoprotein ligand-1 (PSGL-1), a known surface glycoprotein that is expressed constitutively on all human peripheral-blood T cells, Cultured peripheral-blood T cells can be differentiated into CLA-bearing cells, which bind both E-selectin and P-selectin, or CLA-negative cells, which bind P-selectin but do not bind E-selectin, suggesting that there is independent regulation of selectin-binding phenotypes, We propose that differential post-translational modification of a single cell-surface receptor, PSGL-1, mediated by fucosyltransferase VII, serves as a mechanism for regulating tissue-specific homing of memory T cells.