The purpose of this study is to establish the presence of an effect of treatment with ONO-2506PO in patients with Alzheimer's Disease, based upon cognitive and global scales.
Inclusion Criteria: * Diagnosis of probable Alzheimer's Disease using NINCDS/ADRDA criteria * Standardized MMSE Score of 13 to 24 points (inclusive) * Modified Hachinski score equal or less than 4 Exclusion Criteria: * Serious systemic disease that may preclude survival to study completion * Other illnesses that may include dementive features