The nature of inflammatory lymphocytes recruited to the CNS has been studied in a model of chronic inflammation. Injection of killed Corynebacterlum parvum into the cortex of the mouse brain produces a circumscribed inflammatory cellular infiltrate around the injection site, and recruited mononuclear inflammatory cells (IC) can be isolated for flow cytometric analysis. The majority of IC were T cells. In comparison with the predominant naive population of mesenteric lymph node T cells, IC T cells express much higher levels of CD44, LFA-1 and ICAM-1, and lower levels of CD45RB, features commonly associated with memory (previously activated) cells. In addition, in contrast to the L-selectin⁺ α6-integrin^low phenotype of naive lymph node T cells, IC T cells lacked L-selectin and were α6-integrin⁻. Mac-1, recently proposed as another marker of memory T cell differentation, was not displayed by IC T cells, suggesting that Mac-1 expression may be heterogeneous among memory T cell subsets. A subset of mesenteric lymph node (MLN) T cells, probably representing activated T cells undergoing the naive to memory transition, but not of IC T cells, expressed high levels of α6-, β7- and αE-integrin. IC and MLN naive T cells expressed comparable levels of α4-integrin, but IC T cells stain poorly with anti-β7 mAbs and with mAb DATK 32, specific for the α4β7 heterodimeric lymphocyte homing receptor for the mucosal addressin MAdCAM-1, suggesting that these inflammatory cells express more α4β1 than α4β7. Consistent with this, in in vitro adhesion assays, brain IC bound better than MLN cells to the α4β1 integrin ligand VCAM-1 and the LFA-1 ligand ICAM-1 but adhered very poorly to the α4β7 ligand MAdCAM-1. These findings are consistent with and extend previous immunohistological studies of T cells in murine experimental autoimmune encephalomyelitis, and demonstrate a distinctive phenotype for lymphocytes being present in the chronically inflamed brain.