Intrinsically disordered proteins are an abundant class of proteins that are disordered in their native state. Among them, the microtubule-associated protein Tau has attracted considerable attention because its fibrillation leads to abnormal intracellular deposits, so-called “paired-helical filaments” (PHFs), that are one of the two hallmarks of Alzheimer disease. It has been proposed that interaction of the protein with water plays a key role in the fibrilization process [1]. Recently, we started studying the dynamics of PHFs and their hydration water in comparison to the monomeric form by elastic incoherent neutron scattering. Our results indicate significantly enhanced mean-square displacements for water around PHFs, compared to water around the monomeric protein [2]. This result suggests differences in water-protein interaction between native and fibrillated tau, which could be at the basis of the suggested stabilizing effect of water during fibrillation. The present proposal is to investigate in greater detail the observed difference, by studying hydration water dynamics around monomeric tau and PHFs by quasi-elastic neutron scattering (QENS) as a function of temperature.