A composition and use thereof for the prophylaxis or treatment of Alzheimer's disease, motor neurone disease, Lewy body disease, Pick's disease or progressive supranuclear palsy. The composition includes an agent which modulates or inhibits tau-tau association and which does not inhibit tau-tubulin binding. In the method the agent is administered to an individual in order to achieve the desired therapeutic effect. Preferably the agent which is administered is a phenothiazine compound.