An isolated humanized antibody, or fragment therof, that specifically binds an epitope in an N-terminal region of a Tau polypeptide may be used for the treatment of a tauopathy, such as frontotemporal dementia (FTD), Alzeimers disease, progressive supranuclear palsy, corticobasal degeneration, or frontotemoral lobar degeneration. Preferably the antibody binds an epitope within residues 15-24 of Tau. Methods of detecting Tau in vitro or in vivo, or monitoring progression of a taupathy, using antibodies which specifically bind an epitope in an N- terminal region of a Tau polypeptide are provided. Methods of determining the amount of extracellular Tau(eTau) in the cerebospinal fluid (CSF) or interstitial fluid (ISF) which is either unbound, or bound to a therapeutic anti- Tau antibody in a patient undergoing therapy with anti-Tau antibodies, comprise contacting a CSF or ISF sample from the patient with an immobilised anti-Tau antibody which competes with the therapeutic antibody, or does not compete with the therapeutic antibody, respectively.
