Cells of the central nervous system (CNS) and immune system communicate regularly. There is a constant surveillance of the intact, healthy CNS by activated T‐cells, and massive infiltration of the CNS by immune cells under pathological conditions such as neurodegeneration or neuroinflammation. Labeling CNS‐infiltrating T‐cells is an essential tool to identify the signals and mechanisms, which mediate the interaction between immune cells and cells of the CNS. In this article, we will present an overview describing currently used cellular markers and demonstrate how these markers have contributed to our current knowledge of CNS inflammation and immune surveillance. GLIA 36:125–136, 2001. © 2001 Wiley‐Liss, Inc.