Abstract: A method of screening an agent for potential use in the treatment of Alzheimer's disease, comprises reacting, in the presence of the agent, tau protein with a suitable sulphated carbohydrate under appropriate conditions to form filaments, and monitoring for the presence of filaments. Tau protein and sulphated carbohydrate, e.g. sulphated glycosaminoglycan, will react under appropriate conditions to form filaments, either paired helical filaments or straight filaments. If filament formation is affected when the reaction is carried out in the presence of an agent being screened, this is possibly due to an interfering, inhibiting or blocking effect of the agent. An agent which inhibits assembly of PHFs in vitro may also have an inhibiting effect in vivo and thus have potential therapeutic value in delaying the dementing effects of Alzheimer's disease. The invention can thus provide a screen to identify agents worthy of further investigation for use in the treatment of Alzheimer's disease.