Receptor-mediated interactions with amyloid β-peptide (Aβ) could be important in the evolution of the inflammatory processes and cellular dysfunction that are prominent in Alzheimer's disease (AD) pathology. One candidate receptor is the receptor for advanced glycation endproducts (RAGE), which can bind Aβ and transduce signals leading to cellular activation. Data are presented showing a potential mechanism for Aβ activation of microglia that could be mediated by RAGE and macrophage colony-stimulating factor (M-CSF). Using brain tissue from AD and nondemented (ND) individuals, RAGE expression was shown to be present on microglia and neurons of the hippocampus, entorhinal cortex, and superior frontal gyrus. The presence of increased numbers of RAGE-immunoreactive microglia in AD led us to further analyze RAGE-related properties of these cells cultured from AD and ND brains. Direct addition of Aβ(1–42) to the microglia increased their expression of M-CSF. This effect was significantly greater in microglia derived from AD brains compared to those from ND brains. Increased M-CSF secretion was also demonstrated using a cell culture model of plaques whereby microglia were cultured in wells containing focal deposits of immobilized Aβ(1–42). In each case, the Aβ stimulation of M-CSF secretion was significantly blocked by treatment of cultures with anti-RAGE F(ab′)₂. Treatment of microglia with anti-RAGE F(ab′)₂ also inhibited the chemotactic response of microglia toward Aβ(1–42). Finally, incubation of microglia with M-CSF and Aβ increased expression of RAGE mRNA. These microglia also expressed M-CSF receptor mRNA. These data suggest a positive feedback loop in which Aβ–RAGE-mediated microglial activation enhances expression of M-CSF and RAGE, possibly initiating an ascending spiral of cellular activation.