Alzheimer's disease is the major cause of dementia in humans. The affected brain shows characteristic abnormal filamentous proteins that accumulate intracellularly as neurofibrillary tangles, and extracellularly as senile plaques, as well as in cerebral blood vessels. The extracellular deposits are an amyloid protein, which is highly insoluble. In our study, we intended to show that the N-terminus of amyloid A4 protein can change in length and sequence in Alzheimer's disease, and possibly in other dementias.