Brain macrophages are a subpopulation of microglial cells which occur in the developing or in the injured CNS. These cells actively contribute to CNS tissue remodeling by acting on neuronal and macroglial lineages. Recruitment of brain macrophages is promoted by transformation of resting microglial phenotypes, infiltration of the tissue by exogenous macrophage precursors and local proliferation of phagocytes. These events are regulated by extracellular signals produced by glial cells or neurons. Studies based on in vitro cell cultures or experimental tissue lesions suggest that the infiltration of phagocytes involves intracerebral production of chemotactic factors acting on monocytes such as chemokines or extracellular matrix proteins. Proliferation of brain macrophages in stimulated by colony-stimulating factors which seem to be primarily secreted by glial cells.