Infiltration of tissues by monocyte-derived macrophages is a prominent component of a wide-range of diseases, including atherosclerosis, glomerulonephritis, encephalitis, infectious diseases, and virtually all syndromes characterized by chronic inflammation. The molecular signals responsible for this directed migration are incompletely understood, but members of the chemokine family, especially the monocyte chemoattractant proteins (MCPs) (MCP-1 to MCP-5) are emerging as key players. Cells that respond to the MCPs do so because they express chemokine receptor 2 (CCR2), the cognate receptor. This review will summarize evidence supporting a key role for CCR2 in the pathogenesis of atherosclerosis, infections with intracellular pathogens, and regulation of the type I adaptive immune response. Microcirculation(2003) 10,259–264. doi:10.1038/sj.mn.7800191