beta A4 deposits occur in the brain of some individuals over 50 years of age. It could be a part of the aging process or indicate a disease found frequently in the elderly. To address this question, beta A4 immunocytochemistry was performed on the brain of 15 nondemented and 5 demented centenarians, some of whom were affected by Alzheimer's disease. We found beta A4 deposits in the parahippocampal and the superior temporal gyri of all the cases, whatever the clinical state. The hippocampus was frequently spared. The lesion density was not correlated with the severity of the mental deterioration. The constant deposition of beta A4 protein in the brain of very old people indicates that this process does not spare a large proportion of this population. This result favors beta A4 accumulation in the brain being an ineluctable age-related process.