Arterial and arteriolar amyloid-beta (A beta) deposition in hereditary cerebral hemorrhage with amyloidosis (Dutch) (HCHWA-D) and Alzheimer disease (AD) cerebral amyloid angiopathy (CAA) were studied as to morphology, extent, and association with mononuclear phagocyte system (MPS) cells using A beta, a-smooth muscle actin, and monocyte/macrophage marker (HLA-DR, CD68, CD11c, CD45) immunohistochemistry.