Plasma assays that reflect Alzheimer’s pathology in brain have now been validated across many studies (1-3) representing an astounding advance in the field. Mass spectrometry-based plasma Aβ42/Aβ40 assays are highly correlated to cerebrospinal fluid assyas and amyloid PET SUVr measures. These blood tests are now being used as pre-screening tests prior to PET scanning to greatly reduce the burden and costs associated with scanning for trial recruitment. It is plausible that plasma assays may even obviate the need for PET scanning. Measurement of phosphotau species such as ptau217 (2) in plasma are tightly correlated to both amyloid and tau pathology and can likewise be used for screening and longitudinal follow-up in trials, potentially indicating downstream effects of candidate therapies targeting amyloid or tau. Preliminary evidence suggests that plasma amyloid and tau assays may allow identification of individuals on the Alzheimer’s disease spectrum even before PET scans become abnormal. The impact of this new technology on AD disease-modifying drug development will be profound. Further, we can foresee the possibility that plasma biomarkers may prove useful in establishing risk prior to any measurable brain pathology, facilitating the advance of primary prevention trials for Alzheimer’s