Histochemical staining for aluminum, using Solochrome azurine or Morin, provided a rapid, simple and reliable means of identifying areas and structures of the brain of interest for closer scrutiny by X-ray microanalysis in patients with amyotrophic lateral sclerosis and parkinsonism-dementia of Guam. Neuronal perikarya, dendritic processes, and the walls of some cerebral vessels were aluminum positive by Solochrome azurine staining. In some cases, the deposition of aluminum was rather diffuse, particularly in the white matter. Fluorescent localization of aluminum using Morin was equally sensitive and specific, but provided less morphological detail than Solochrome azurine. Confirmation of histochemical detection of aluminum was achieved by examining adjacent tissue sections using wavelength-dispersive spectrometry coupled to a computer-controlled electron beam X-ray microprobe. Although the minimum detectable limits for aluminum by these histochemical procedures are unknown, the lower detection limit of our X-ray microanalytical technique is 10-100 ppm dry weight. Solochrome and Morin staining, as verified by X-ray microanalysis, afford a useful and reliable means of surveying multiple anatomical regions for aluminum deposition in naturally occurring and experimentally induced neurodegenerative disorders.