The macrophage scavenger receptor is a multifunctional receptor whose ligands include oxidized low density lipoprotein (LDL), as well as several other polyanionic macromolecules. Although the capacity of the receptor to bind modified LDL has implicated it in the process of atherosclerosis, its physiological role remains uncertain. We have examined human brain for expression of macrophage scavenger receptor as part of ongoing studies of lipoprotein receptors in the central nervous system. The receptor is expressed on microglia, but not on astrocytes, neurons, or vessel-associated structures. In Alzheimer disease, there is strong expression of the scavenger receptor in association with senile plaques.