The agents that are available at present for the management of Alzheimer's disease treat only the symptoms of neurodegeneration and, at best, result in modest, short-term improvements in cognitive function. Immunotherapy represents one of the first tests of the amyloid hypothesis in the clinic, and is an evolving approach to the treatment of Alzheimer's disease that offers a genuine opportunity to modify disease progression. Although initial clinical trials of one approach met with some setbacks, active or passive immunization holds great potential for treating or even preventing Alzheimer's disease.