Using leucocyte cultures, the chromosomes were studied in eight cases of Alzheimer’s disease. The material included two cases of the familial form, five cases of the sporadic form, and one case of a mongol having developed the disease. Not a single cell in any of the cases contained big acentric chromosomes, an aberration recently suggested to be specific to Alzheimer’s disease. In the present study, excluding the mongol case, the chromosomal variation did not differ from that normally found during senescence. Thus, there was no counterpart to the increased loss of C chromosomes in hypodiploid variant cells, earlier described in cases of senile dementia. The cytogenetical observations in the present cases of familial and sporadic Alzheimer’s disease offered no explanations for the concurrence between this disease and Down’s syndrome.