There is now substantial evidence indicating that an accumulation of aluminum occurs in grey matter in diseases associated with Alzheimer neurofibrillary degeneration. Four principle sites of aluminum accumulation have been identified in Alzheimer's disease: DNA containing structures of the nucleus, the protein moieties of neurofibrillary tangles, the amyloid cores of senile plaques and cerebral ferritin. Consideration of the extensive information now available on the toxic effects of aluminum in these four loci strengthens the hypothesis that aluminum could be important in the pathogenesis of this neurodegenerative process. The evidence, however, does not support an etiological role for aluminum in Alzheimer's disease. The primary pathogenic events responsible for Alzheimer's disease are presumed to have affected the genetically determined barriers to aluminum resulting in increased amounts of this toxic element to vulnerable target sites.