Abstract: Microglia are the CNS macrophage and are a primary cellular component of plaques in Alzheimer's disease (AD) that may contribute to the oxidative stress associated with chronic neurodegeneration. We now report that superoxide anion production in microglia or macrophages from 3 different species is increased by long term exposure (24 hours) to Aβ peptides. Since Aβ competes for the uptake of opsonized latex beads and for the production of superoxide anion by opsonized zymosan, a likely site of action are membrane receptors associated with the uptake of opsonized particles or fibers. The neurotoxic fibrillar peptides Aβ (1–42) and human amylin increase radical production whereas a non‐toxic, non‐fibrillar peptide, rat amylin, does not. We also report that the effect of Aβ peptides on superoxide anion production is not associated with a concomitant increase in nitric oxide (NO) production in either human monocyte derived macrophages (MDM) or hamster microglia from primary cultures. Since NO is known to protect membrane lipids and scavenge superoxide anion, the lack of Aβ‐mediated induction of NO production in human microglia and macrophages may be as deleterious as the over‐production of superoxide anion induced by chronic exposure to Aβ peptides.