Abstract: The invention pertains to the development of antibodies that specifically bind amyloid beta protein (Abeta) in its protofibril conformation. The invention also comprises methods of using anti-Abeta protofibril antibodies to diagnose or treat Alzheimer's disease, Down's syndrome Lewybody dementia, vascular dementia, and other neurodegenerative disorders. Furthermore, the invention pertains to the use of anti-Abeta protofibril antibodies to screen and identify substances that will modulate protofibril activity or formation in vitro or in vivo. The invention also pertains to methods for synthesising pure Abeta protofibril antigens as well as to a method for stabilising Abeta protofibrils antigens as well as to a method for stabilising Abeta protofibrils.