Chemokines constitute a superfamily of small (8-10 kDa), inducible, secreted, pro-inflammatory cytokines that are involved in a variety of immune and inflammatory responses as well as in viral infection. Chemokines act primarily as chemoattractants and activators of specific types of leukocytes. Some members of this family were initially identified on the basis of their biological activities (e.g., IL-8, GRO), others were discovered using subtractive hybridization (e.g., RANTES) or signal sequence trap (e.g., PBSF/SDF-1)11 cloning strategies. They attract and activate leukocytes and regulate diverse cellular systems and organs ranging from blood vessels to the central nervous system.