A traumatic injury to the adult mammalian central nervous system (CNS) results in reactive astrogliosis and the migration of hematogenous cells into the damaged neural tissue. Chemokines, a novel class of chemoattractant cytokines, are now being recognized as mediators of the inflammatory changes that occur following injury. The expression of MCP-1 (macrophage chemotactic peptide-1), a member of the p family of chemokines, has recently been demonstrated in trauma in the rat brain (Berman et al.: J Immunol 156:3017-3023, 1996). Using a stab wound model for mechanical injury, we studied the expression of two other p chemokines: RANTES (Regulated on Activation, Normal T cell Expressed and Secreted) and MIP-1 p (macrophage inflammatory protein-1 beta) in the rat brain. The stab wound injury was characterized by widespread gliosis and infiltration of hematogenous cells. Immunohistochemical staining revealed the presence of RANTES and MIP-1 p in the injured brain. RANTES and MIP-1 j3 were both diffusely expressed in the necrotic tissue and were detected as early as 1 day post-injury (dpi). Doublelabeling studies showed that MIP-1 p, but not RANTES, was expressed by reactive astrocytes near the lesion site. In addition, MIP-1 p staining was also detected on macrophages at the site of injury. The initial expression of the chemokines closely correlated with the appearance of inflammatory cells in the injured CNS, suggesting that RANTES and MIP-1 (3 may play a role in the inflammatory events of traumatic brain injury. This study also demonstrates for the first time MIP-1 f3 expression in reactive astrocytes following trauma to the rat CNS.