It is now known that Alzheimer's disease starts decades prior to the appearance of clinically detected disease. This fact presents a window of opportunity for therapeutic intervention prior to the development of significant cognitive decline. Several modalities have demonstrated the ability to detect pre-clinical disease, such as cerebral amyloid imaging and lumbar puncture. These are cost prohibitive for routine clinical use, or in the case of lumbar puncture biomarkers, invasive for patients. This emphasizes the need for a biomarker that would indicate early Alzheimer's, that would be minimally invasive and inexpensive. The Coleman/Mastroeni lab and the Sierks lab, both at ASU have published evidence for two different blood based biomarkers capable of detecting pre-symptomatic disease. We propose to validate these two conceptually different blood biomarkers of Alzheimer's disease against each other and against PET data generated from an on-going amyloid PET imaging study being conducted by Dr. Eric Reiman. We hypothesize that Both multivariate analysis of transcripts expressed by peripheral blood leukocytes and plasma protein biomarkers will correlate with each other, and with brain amyloid detected by PET imaging. These data will provide evidence of a non-invasive and cost-sensitive method of diagnosis early in the course of disease.