Alzheimer's disease is a progressive neurodegenerative disease characterized by the development of large numbers of neurofibrillary tangles in certain neuronal populations. Aluminum salts inoculated into experimental animals produce neurofilamentous lesions which are similar, but not identical, to the neurofibrillary tangle of Alzheimer's disease. Although a few reports suggest evidence of increased amounts of aluminum in the brains of Alzheimer's disease victims, such bulk analysis studies have been difficult to replicate. Using scanning electron microscopy with x-ray spectrometry, we have identified accumulations of aluminum in neurofibrillary tangle-bearing neurons of Alzheimer's disease. Similar accumulations have been identified in the neurofibrillary tangle-bearing neurons found in the brains of indigenous natives of Guam who suffer from parkinsonism with dementia and from amyotrophic lateral sclerosis. This ongoing research still cannot ascribe a causal role of aluminum in the pathogenesis of the neurofibrillary tangle; however, it does suggest that environmental factors may play an important part in the formation of this abnormality.