Morphological abnormalities of the cortical microvessels have been reported in Alzheimer's disease (AD), but not in Binswanger's disease (BD), a form of vascular dementia. Therefore, we compared the capillary beds in AD and BD brains, using a modified Gallyas silver impregnation method and immunohistochemistry for beta amyloid. Eight autopsied brains with AD and seven with BD were compared with six control brains. The cortical microvessels in AD were frequently narrowed, and torn off, especially in close proximity to the senile plaques. The capillary densities in AD were significantly decreased as compared with the control brains. In contrast, there were no significant changes in the capillary densities and their morphologies in BD brains. Immunohistochemistry for beta amyloid revealed numerous deposits in the vascular wall and perivascular neuropil exclusively in AD brains. Cortical microvascular changes in AD and their absence in BD may indicate a role of beta amyloid for the microvessel pathology in AD.