We describe an investigation of corpora amylacea (CA) in the brain tissue of Alzheimer's disease (AD) cases and normal ageing controls, using both light (LM) and electron (EM) microscopic techniques. CA populations were shown by routine histological staining of LR White resin sections with methenamine silver and PAS, and were compared with those shown by immunocytochemistry using antibodies to tau, GFAP, tubulin, ubiquitin, beta-amyloid and serum amyloid P component in serial sections. All CA were immunoreactive with anti-tau and all were unreactive with anti-beta-amyloid. Most were immunoreactive with anti-serum amyloid P component, although this was often weak in AD. CA from normal ageing brain were immunoreactive for proteins that are associated with the neuronal cytoskeleton and cell injury. CA from AD brain shared some of these but differed from those in normal ageing brain by being in much larger number and more variable in their immunoreactivity. In all CA, X-ray microanalysis illustrated the presence of the metallic elements Ca, Fe and Cu. Aluminium, often associated with AD, was not present, even in CA from AD brain. Phosphorus and sulphur, probably from phosphorylated proteins associated with degenerating cytoskeleton elements, were usually detected. In AD brain, the greater numbers of CA and their variable biochemical and elemental composition, when compared with CA in the normal ageing brain, suggests that they may derive from a number of sources both neuronal and glial as a result of the neurodegenerative disease.