The microtubule-associated protein tau has a critical role in Alzheimer disease and other tauopathies. In its hyperphosphorylated form, tau impairs neuronal functions and eventually causes neuronal demise. In vivo, tau hyperphosphorylation is linked to aggregated forms of tau. In turn, aggregated tau can form a misfolded tau “seed” with characteristic similar to prions. In a prion-like state, tau can induce aggregation of monomeric endogenous tau. These features have been termed prion-like and have caught a lot of attention in the field. A body of evidence supports that tau aggregates can move between synaptically connected cells, where physiological tau can be induced to aggregate and misfold into a pathological state. My research is focused on small extracellular vesicles such as exosomes. I recently reported that only cells undergoing intracellular tau aggregation could release extracellular vesicles containing tau seeds, with ability to induce tau misfolding and aggregation in naïve healthy cells (Polanco et al., J Biol Chem. 2016). Here I report a follow-up study where the plasma membrane of tau biosensor cells was tracked during endocytosis of exosomes using different fluorescent tags. The membranes of endocytic vacuoles appeared intact during the formation of exosome-induced tau inclusions. Fusion with lysosomes occurred during the formation of tau inclusions and did not halt the tau-aggregation process. Therefore, we tested in several ways whether lysosome function was required for the induction of tau aggregation. First, overexpression of RAB7, required for fusion of late endosomes with lysosomes, strongly increased tau aggregation. Second, RAB7 knockdown decreased tau aggregation, indicating that the fusion with lysosomes strengthens tau aggregation. Furthermore, alkalinisation of lysosomes also showed a negative effect on tau aggregation. All together support that lysosomal function is required for tau aggregation induced by exosomes probably by increasing the escape of tau seeds from the endolysosome.