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 is a 39-42 amino acid 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 early-onset AD. A? generation depends on proteolytic cleavage of the amyloid precursor protein (APP) by two unknown proteases: ?-secretase and ?-secretase. Recent study suggested that a transmembrane aspartic protease, termed beta-site APP-cleaving enzyme (BACE), functionally acts as the ?-secretase. This antibody recognizes N-terminal of A? 40 and A? 42 specifically.