The frequency of antinuclear antibodies was evaluated in older men and women aged 60 to 100 years with presumptive diagnoses of chronic brain syndrome or dementing illness. Thirteen per cent of the women and none of the men with organic brain syndrome had positive titers, compared to 3 per cent for older men and women aged 60 to 89 years evaluated in a medical clinic population. It would appear to be valuable to evaluate the significance of antinuclear antibodies and other autoantibodies in the pathogenesis of dementing illness in the elderly.