Chemokines are a novel class of small, basic, proinflammatory cytokines. They are associated with leukocyte chemoattraction, ie, directional migration of lymphocytes, monocytes, eosinophils, and neutrophils (Wolpe et al., 1989; Oppenheim et al., 1991; Miller et al., 1992; Tani et al., 1994). Based on structural and genetic characteristics chemokines are divided into two subfamilies (Lindley et al., 1993): i) CXC or a-family, where two positionally conserved cysteine residues are separated by one amino acid, and ii) CC or P-family, in which the two cysteine residues are adjacent. In human, the CXC and CC chemokines are encoded by chromosome 4 and 17, respectively. Importantly, the chemokines are target selective, and members of the two subfamilies differ functionally. The a-chemokines are chemotactic largely for neutrophils whereas those of the P-family act primarily on monocytes and T-cells. Interestingly, P-chemokines also act on basophils and eosinophils. Representative members of the CXC family are platelet factor 4 (PF4), P-thromboglobulin (P-TG), IL-8, gro, IP-10, MIG, and ENA-78, whereas those of the CC family includes MIP-la, MIP-1 P, RANTES, MCP-UJE, HC-14, C-10, and 1-309. None of the chemokines except RANTES, P-TG, and PF-4 are expressed in resting cells. All are rapidly induced in response to various inflammatory and mitogenic stimuli. Homologous chemokine genes and products have been described in both human and mice. In this review, we focus on expression and regulation of two chemokines, MCP-I and IP-10, under inflammatory conditions in the central nervous system.