Senile plaques in the brains of Alzheimer's disease (AD) were examined by confocal laser scanning microscopy (CLSM) with the following three findings. First, in sections stained with Congo red, the serial CLSM images of optical sections clearly revealed that a classic plaque is composed of a plaque core and a corona. Radially arranged process-like structures, corresponding to bundles of amyloid fibrils, formed amyloid cores and stronger signals were detected in the center of some cores. Second, in sections stained with Congo red and anti-glial fibrillary acidic protein (GFAP), reactive astrocytes were found around the senile plaques and many astrocytic processes surrounded the plaque cores and some processes had penetrated into them. Third, three-dimensional reconstruction on classic plaque revealed that the surface of classic plaque showed a 'coral-like' appearance.