Evaluate the Efficacy and Safety of ABT-126 in Subjects With Mild to Moderate Alzheimer's Disease on Stable Doses of Acetylcholinesterase Inhibitors

This is a Phase 2 study designed to evaluate the efficacy and safety of ABT-126 in
approximately 420 adults with mild to moderate Alzheimer's disease who are taking stable
doses of acetylcholinesterase inhibitors. Subjects will be randomized to one of two ABT-126
dose arms or placebo for a 24-week treatment period.

Inclusion Criteria:

- The subject and caregiver must voluntarily sign and date an informed consent. If the
subject does not have the capacity to provide informed consent, full informed consent
must be obtained from the subject's representative and assent must be obtained from
the subject.

- The subject is a male or female between the ages of 55 and 90 years, inclusive, at
Screening Visit 1. Main Inclusion (Continued):

- The subject meets the Neurological and Communicative Disorders and Stroke/Alzheimer's
Disease and Related Disorders Association (NINCDS/ADRDA) criteria for probable AD.

- The subject must be receiving a stable dose of an AChEI (donepezil or rivastigmine)
for at least 90 days prior to Screening Visit 1.

- The subject has a Mini-Mental Status Examination (MMSE) total score of 12 to 24,
inclusive, at Screening Visit 1.

- The subject has a Cornell Scale for Depression in Dementia (CSDD) score ≤ 10 at
Screening Visit 1.

- The subject has a Modified Hachinski Ischemic Scale (MHIS) score of ≤ 4 at Screening
Visit 1.

- With the exception of a diagnosis of mild-to-moderate Alzheimer's disease and the
presence of stable medical conditions, the subject is in general good health, based
upon the results of medical history, physical examination, vital signs, laboratory
profile, and a 12-lead electrocardiogram (ECG).

- The subject has an identified, reliable caregiver who will provide support and ensure
compliance with the study medication and procedures, and provide accurate information
about the subject's status during the study.

Exclusion Criteria:

- The subject has taken galantamine or memantine within 60 days prior to Screening
Visit 1.

- The subject has received excluded concomitant medications.

- The subject has clinically significant abnormal laboratory values at Screening Visit
1 as determined by the investigator.

- The subject has a history of any significant neurologic disease other than
Alzheimer's disease including Parkinson's disease, multi-infarct or vascular
dementia, Huntington's disease, normal pressure hydrocephalus, progressive
supranuclear palsy, multiple sclerosis, any seizures, mental retardation or a history
of significant head trauma followed by persistent neurologic deficits or known
structural brain abnormalities.

- In the opinion of the investigator, the subject has any clinically significant
uncontrolled medical or psychiatric illness.