Vessels affected by amyloid angiopathy in patients with Alzheimer's disease also displayed intense acetylcholinesterase and butyrylcholinesterase activity when examined by light and electron microscopy. The enzymatic properties of the vessel-bound cholinesterases were identical to those of the cholinesterases associated with senile plaques and neurofibrillary tangles. This cholinesterase activity is of unknown origin but represents one of the very few features common to all the major pathological markers of Alzheimer's disease.