Two new papers were published this week in PNAS. The first one describes the existence of distinct “strains” of Aβ aggregates in the brains of Alzheimer’s disease patients. In this paper we demonstrate for the first time that, like different strains of PrP^Sc, the properties of Aβ strains are maintained following multiple passages in mice. The second paper describes the generation of distinct strains of synthetic Aβ aggregates.