A Study of RO4602522 in Participants With Moderate Severity Alzheimer Disease on Background Alzheimer Disease Therapy

Inclusion Criteria:

   - Probable Alzheimer disease, based on the National Institute of Neurological and
   Communicative Disorders and Stroke (NINCDS)/Alzheimer's Disease and Related Disorders
   Association (ADRDA) and Diagnostic and Statistical Manual of Mental Disorders-Fourth
   Edition (DSM-IV-TR) criteria

   - Mini-Mental State Exam (MMSE) score at screening between 13 and 20, inclusive

   - Body mass index (BMI) between 18 and 36 kilograms per square meter (kg/m^2)
   (inclusive) at screening

   - Modified Hachinski Ischemia Score of less than or equal to (
   - Participants with Cornell Scale for Depression in Dementia (CSDD) scores    screening

   - Receiving treatment with donepezil, rivastigmine, galantamine or any AChEIs in
   combination with memantine for at least 4 months before screening, with their dose and
   formulation stabilized at least 3 months before screening. All formulation and dosages
   are allowed except donezepil 23 mg (alone or in combination)

   - Females of childbearing potential must have a negative pregnancy test and must agree
   to use effective contraception

   - Generally healthy and ambulatory or ambulatory-aided (i.e., walker or cane)

   - Have a reliable caregiver or some other identified responsible person who has frequent
   contact with the participant

Exclusion Criteria:

   - Any neurological or psychiatric condition that may occur currently or during the
   course of the study that can impair cognition or functioning that is not associated
   with Alzheimer's disease

   - Background of mental retardation

   - Uncontrolled behavioral symptoms incompatible with compliance or evaluability

   - Alcohol and/or substance abuse or dependence (DSM-IV-TR) in the past 2 years, except
   nicotine use which is allowed. However, smokers treated with nicotine replacement
   therapy or bupropion are excluded

   - Unstable or poorly controlled hypertension as assessed by the investigator regardless
   of whether or not the participant is taking antihypertensive medications

   - Unstable or clinically significant cardiovascular disease that could be expected to
   progress, recur, or change during study period to such an extent that it could bias
   the assessment of the clinical or mental status of the participant

   - Inadequate hepatic, renal or thyroid function

   - Positive for hepatitis B, hepatitis C or human immunodeficiency virus (HIV) infection

   - Poorly controlled diabetes (glycosylated hemoglobin [HbA1c] greater than or equal to
   [>/=] 9 percent at screening)

   - Requiring nursing home care. Participants living in assisted living facilities are
   allowed if a reliable caregiver is available (see inclusion criteria)

   - Current treatment for Alzheimer's disease other than those listed in inclusion
   criteria

   - Participation at any time in an active Alzheimer's disease vaccine study

   - Participation in a passive Alzheimer's disease immunization study less than 1 year
   before screening except for a) participants where documented medical history indicate
   that they were randomized to the placebo group in these studies, b) participants
   treated with bapineuzumab where a 6-month exclusion period applies

   - Recent (   (selective or not) including selegiline or rasagiline

   - Antidepressant treatments are not allowed except for citalopram up to 20 mg daily,
   escitalopram up to 10 mg daily, paroxetine up to 30 mg daily, sertraline up to 100 mg
   daily and trazodone up to 100 mg daily. If treated with one of these antidepressants,
   the treatment should be present for at least 6 weeks at screening. All other
   antidepressants including other SSRIs, tricyclic antidepressants (TCAs),
   serotonin-norepinephrine reuptake inhibitors (SNRIs), St. John's wort and bupropion
   are excluded

   - Anti-psychotic use within 4 weeks before screening is not permitted except risperidone
   up to 1.5 mg/day, quetiapine up to 100 milligrams per day (mg/day), olanzapine up to 5
   mg/day, and aripiprazole up to 10 mg daily

   - Anxiolytics/ hypnotics use is not permitted except for benzodiazepines of short or
   intermediate half-life for anxiety/sleeping disorders. Zolpidem (up to 5 mg/day),
   zopiclone (up to 7.5 mg/day), eszopiclone (up to 2 mg/day), trazodone (up to 50
   mg/day, at bedtime) or zaleplon (up to 5 mg/day) is permitted for insomnia

   - Anti-Parkinson's agents within 2 weeks before screening are not permitted

   - Recent (less than 4 weeks prior to screening) or concomitant use of anticonvulsants

   - Anticholinergics/ antihistaminics within 2 weeks before screening are not permitted,
   except i) if used episodically more than 3 days before the screening cognitive
   measurement, ii) non-sedating antihistaminic medications (without anticholinergic
   effects such as cetirizine) or peripheral anticholinergics without central
   anticholinergic effects (such as, trospium for the treatment of hyperactive bladder),
   which are permitted

   - Recent (less than 1 week prior to screening) or concomitant use of opioid drugs
   (tramadol, methadone, propoxyphene, or meperidine), cyclobenzaprine and
   dextromethorphan

   - Concomitant use of sympathomimetic drugs, including sympathomimetics in local
   anesthetics and ephedra supplements