Disclosed is a method for diagnosing Alzheimer's disease (AD) wherein Aβ-specific antibodies in a biological sample of a person that is suspected of having AD are detected comprising the following steps: —contacting the sample with Aβ-aggregates or with particles having Aβ-aggregate like surfaces and allowing the Aβ-specific antibodies to bind to the Aβ-aggregates, and —detecting the Aβ-specific antibodies bound to the Aβ-aggregates by a single particle detection technique, preferably by fluorescence activated cell sorting (FACS)； and wherein the amount of Aβ-specific antibodies detected is compared with the amount in a sample of known AD status.
