Alzheimer's disease (AD) is the most common form of dementia in the elderly. The neuropathological hallmarks are neurofibrillary tangles and senile plaques. The major protein component of the plaques consists of 39-42 amino acids peptide (-amyloid/A). A occurs in two predominant forms with different COOH-termini, A 40 and A 42, and overproduction of A 42 has been suggested to be the cause of familial earlyonset AD. A generation depends on proteolytic cleavage of the amyloid precursor protein (APP) by two proteases: -secretase and -secretase. Recent study suggested that a transmembrane aspartic protease, termed -site APP-cleaving enzyme (BACE), functionally acts as the -secretase.