Studies conducted in many laboratories over the past several years have resulted in the identification and initial characterization of a large superfamily of structurally and functionally related inflammatory cytokines. This superfamily currently includes 14 distinct members: platelet factor 4, beta-thromboglobulin, neutrophil activating peptide-1/interleukin-8, gro, IP-10, mig, ENA-78, macrophage inflammatory proteins-1 alpha and -1 beta, monocyte chemoattractant protein-1/JE, RANTES, HC-14, C-10, and I-309. Although numerous biological activities have been assigned to these molecules, a common theme is their ability to stimulate the chemotactic migration of distinct sets of cells, including neutrophils, monocytes, lymphocytes, and fibroblasts. Accumulating evidence indicates that these molecules play important roles in mediating cell recruitment and activation necessary for inflammation and the repair of tissue damage.