The role of aluminum in the etiology of Alzheimer's disease remains controversial because of the contradictory results reported in the field. Measurements on fixed and stained samples in which disease-related plaques and tangles can be identified are criticized for possible elemental redistribution and contamination. Even with a sandwich-section technique, in which plaques in an unfixed, unstained section can be located from their position in two adjacent stained sections, uncertainty remains about structure and, therefore, also about meaningful Al concentrations. The effect of a modified thioflavin stain on elemental distributions in cryosections of Alzheimer's disease brain tissue has been examined, using energy- dispersive X-ray spectroscopy (EDS) to analyze plaque composition before and after staining. It was found that, although staining alters the overall composition, peaks for Al and other elements such as Si and Fe are relatively unchanged by staining. Based on this finding, the relationship of Al to plaque structure is being investigated in thioflavin-stained sections.