The principal fibrous component of neurofibrillary pathology in Alzhei
mer's disease, the paired helical filament, is formed from hyperphosph
orylated microtubule-associated protein tau. Here we show that recombi
nant tan protein either in a non-phosphorylated state or following pho
sphorylation with brain extract can be assembled in vitro into filamen
ts resembling those seen in Alzheimer's disease.