Alzheimer's Disease (AD) is characterized by the presence of extracellular senile plaques (SPs) and intracellular neurofibrillary tangles (NFT) in the brain. The major protein component of SPs is beta Amyloid peptide (AB) 40 AND 42(43). AB 42 is more prone to aggregate than AB 40. Therefore the initial AB deposition begins with AB 42(43) but not with AB 40. AB 42(43)-positive and AB 40-negative plaques may represent early-stage diffuse type SPs, and AB 40-positive plaque appears in the advanced stage, especially more often in the cored portion of the mature plaque.The High Sensitivity kits have a detection sensitivity of about 10 times higher than the original kits, and the dynamic range is from 0.1 to 20.0 pmol/L.