We have investigated the cerebral cortex of Alzheimer's disease in which small infarcts are found on postmortem neuropathological examination. In areas that have been subjected to recent ischemia, immunohistochemical staining for amyloid β-protein (Aβ) is much less intense than in the non-ischemic surround. However, the infiltrating brain macrophages contain granules immunopositive for C-terminal fragments of Aβ. The immunohistochemical profile indicates that Aβ in these granules lacks epitopes in the N-terminal fragments. These data suggest that appropriately stimulated macrophages can phagocytose Aβ deposits and that digestion of the N-terminal region is an early consequence of this phagocytosis.