Several neurodegenerative diseases, including Alzheimer's disease (AD), have etiology connected to abnormal protein self association. Copper-induced striking differences in amyloid-β40 aggregation, distinct from spontaneous self association, prompted us to study whether amyloid-β40 aggregation could be applied to differentiate between platelet poor plasma ultrafiltrates obtained from AD and control samples. We report, based on 20 AD and 18 age-matched controls, a significant difference in the concentration of short fibers induced by ultrafiltrated plasma from AD compared to control samples. The observed effect was independent of copper and other EDTA chelatable ions.