To address the association of apoE (overall and its subspecies in the fraction of plasma without HDL [non-HDL], in HDL, and in HDL that contains or lacks apoC3 or apoJ) with cognitive function, incidence of dementia, and AD, this study measured the apoE concentration in these lipoprotein subspecies in a prospective, well-phenotyped population of older adults. The gene discussed is APOE; the disease is dementia.