There are many medical conditions that increase brain Al concentrations without producing the dementia or neuronal degeneration (with "paired-helical filaments" [PHFs]) typical of Alzheimer's disease (AD). Aluminum accumulations have been found in the nuclei of PHF-containing neurons in the brains of AD patients and elderly normal controls. We have, however, found no elevations of Al concentrations in the serum, cerebrospinal fluid, or hair in AD patients. These findings suggest that Al alone is not a "cause" of AD. Aluminum may be just a "marker" of PHF-bearing neurons, or AD patients may be "vulnerable" to Al neurotoxicity on the basis of some other neuronal dysfunction allowing Al to enter neuronal nuclei. It is too soon to tell whether any of the variety of experimental anti-Al approaches currently being evaluated have any effect on the rate of progression of AD symptoms.