The in vivo functional activity of central nervous system (CNS) noradrenergic, vasopressinergic and cholinergic systems will be evaluated in vivo in patients with Alzheimer's disease (AD) and in comparison groups of patient's with multiinfarct dementia and both elderly and young normal subjects. These neuronal and endocrine systems appear abnormal in AD and affect behaviors impaired in AD. Three major questions will be addressed: 1) Is there decreased alpha-2 mediated suppression of CNS noradrenergic systems in AD? This question will be addressed by measuring the response of norepinephrine (NE) in cerebrospinal fluid (CSF) and plasma to the alpha-2 agonist clonidine. 2) Does the observed decrease in CSF agrinine vasopressin in AD reflect the cholinergic deficiency of AD? This questions will be addressed by measuring the response of AVP in CSF to the cholinesterase inhibitor physostigmine and to hypertonic saline. 3) Can the cholinergic deficiency of AD be documented in AD antemortem via blunted plasma neuroendocrine responses to increased CNS cholinergic stimulatory regulation (AVP, beta endorphin, NE, epinephrine and growth hormone) to physostigmine. These studies should increase knowledge of AD pathophysiology and suggest clinically useful diagnostic and therapeutic approaches to this disorder.