CCL21, which is a member of the family of CC-Chemokines, has a unique 36 (murine) or 37 (human) amino acid carboxyl-terminal extension not seen in other chemokines. CCL21 selectively stimulates the chemotaxis of adult T lymphocytes and is expressed preferentially in lymph node tissue. CCL21 is critical for adult T cell adhesion to high endothelial venules in lymph nodes, a rate-limiting step for T cell trafficking through nodal tissue.