We investigated the plasma cortisol levels at a fasting state in elderly female Alzheimer's disease (AD), vascular dementia (VD), and non-demented subjects (n=66, 28 and 21, respectively). Twenty-eight AD subjects were followed for 40 months. The plasma cortisol levels in AD and VD subjects were significantly higher than those of non-demented subjects at baseline. In AD subjects in relatively early stages of the disease [Mini-Mental State Examination (MMSE)], at baseline, high plasma cortisol led to rapid declines in MMSE scores over a 40-month period.