Beta-amyloid peptide (Abeta), the major constituent of amyloid plaques in thebrains of Alzheimer"s patients, is thought to be the cause of Alzheimer"s Disease(AD). Alzheimer"s diseased brains show significant levels of Abeta (11-40) andAbeta (11-42). The beta-secretase enzyme or Beta-amyloid precursor protein-cleavingenzyme (BACE) generates the N terminus of beta amyloid, producing full-length Abeta (1-40 and 1-42) and/or truncated Abeta (11-40 and 11-42). The abundance of Abeta(11-40 and 11-42) produced by BACE suggests that they might be playing animportant role in Alzheimer"s disease pathogenesis.