The purpose of this study is to assess the safety and tolerability of multiple doses of AAB-001 passive immunization in patients with mild to moderate Alzheimer's disease (AD).

The humanized monoclonal antibody, AAB-001, which binds to and clears beta amyloid peptide, is designed to provide antibodies to beta amyloid directly to the patient, rather than requiring the patient to mount his/her own individual response. It is believed that this approach may eliminate the need for the patient to mount an immune response to beta amyloid. Animal studies have shown that this approach is equally effective in clearing beta amyloid from the brain as traditional active immunization methods.

This is a multicenter, double-blind, placebo controlled, randomized, outpatient, multiple ascending dose study in male and female patients aged 50 to 85 years with mild to moderate AD. Approximately 30 study sites will be involved. Patients will be randomized to receive either AAB-001 or placebo. Each patient's participation will last approximately 2 years.

Inclusion Criteria:

• Diagnosis of probable AD
• Age from 50 to 85 years
• Rosen Modified Hachinski Ischemic score less than or equal to 4
• Magnetic resonance imaging (MRI) scan consistent with the diagnosis of AD
• Fluency in English
• Stable doses of medications

Exclusion Criteria:

• Significant neurological disease other than AD
• Major psychiatric disorder
• Significant systemic illness
• History of stroke or seizure
• Weight greater than 120 kg (264 lbs.)
• History of autoimmune disease
• Smoking more than 20 cigarettes per day
• Anticonvulsants, anti-Parkinson's, anticoagulant, or narcotic medications
• Prior treatment with experimental immunotherapeutics or vaccines for AD
• Presence of pacemakers or foreign metal objects in the eyes, skin, or body