A Study of RO5313534 as Add-on to Donepezil Treatment in Patients With Mild to Moderate Alzheimer's Disease

Inclusion Criteria: * adult patients, \>/=50 years of age; * probable Alzheimer's disease; * MMSE score at screening of 13-22; * under stable donepezil treatment given at a fixed dose of 5 or 10mg daily for \>=4 months prior to baseline; * not requiring nursing home care, but looked after by a caregiver/carer. Exclusion Criteria: * dementia due to condition other than Alzheimer's disease; * other significant neurological disorder; * untreated/non-stabilized major depressive disorder; * bipolar disorder, schizophrenia, or any other serious psychiatric condition.