The purpose of this study is to demonstrate that AZD3480 improves cognition in patients with mild or moderate Alzheimer's disease, to assess the safety and tolerability of ZAD3480 and to define the optimal dose(s) to be used in future trials.

Inclusion Criteria:

• Provision of informed consent from patient and caregiver
• Clinical prognosis of probable Alzheimer's disease
• Patient must have a caregiver visiting the patient at least three times weekly

Exclusion Criteria:

• Significant neurologic disease or dementia other than Alzheimer's disease
• Major depressive disorder, other major psychiatric disorder
• Use of acetylcholinesterase inhibitor or memantine for treatment of Alzheimer's disease within 8 weeks prior to enrollment
• Impaired vision and/or hearing making cognitive testing difficult