The formation, growth, and maturation of brain amyloid “senile” plaques are essential pathological processes in Alzheimer's disease (AD) and key targets for therapeutic intervention. The process of in vitro deposition of Aβ at physiological concentrations onto plaques in AD brain preparations has been well characterized, but is cumbersome for drug discovery. We describe here a high-throughput screen for inhibitors of Aβ deposition onto a synthetic template (synthaloid) of fibrillar Aβ immobilized in a polymer matrix. Synthaloid is indistinguishable from plaques in AD brain (the natural template) in deposition kinetics, pH profile, and structure-activity relationships for both Aβ analogs and inhibitors. Synthaloid, in contrast to current Aβ aggregation screens, accurately predicted inhibitor potency for Aβ deposition onto AD cortex preparations, validating its use in searching for agents that can slow the progression of AD and exposing a previously inaccessible target for drug discovery.