The invention provides a method for the treatment of a patient having a more severe form of Alzheimer's disease (AD), where the severe form of AD is characterized by pathogenic deposits of amyloid beta peptide (Aβ), comprising the administration of an immunogenic fragment of Aβ capable of inducing an immune response in the form of antibodies to specific to the pathogenic deposits of Aβ and, in particular, to neurotoxic forms of Aβ including N-terminally truncated forms of Aβ. The invention further provides a method for selecting a suitable immunogenic fragment of Aβ for the treatment of a more severe form of AD.