Patients with Alzheimer's disease and nondemented elderly control subjects participated in studies of cortisol secretion during sleep and at 9: 00 am and were given dexamethasone suppression tests (DSTs) and lumbar punctures. Nocturnal and 9: 00 am cortisol concentrations were significantly higher in the demented patients. CSF MHPG negatively correlated with mean nocturnal cortisol. The most severely demented patients had the highest 9: 00 am and mean nocturnal cortisol concentrations. DST results did not distinguish samples with substantially different nocturnal cortisol concentrations. These results suggest that measurements of basal plasma cortisol concentrations and dexamethasone suppression provide different information but support the notion of somewhat higher than normal cortisol concentrations in Alzheimer's disease patients.