The purpose of this study is to test if the investigational medication, ABT-384, is a safe and effective treatment for adults with mild-to-moderate Alzheimer's Disease.

This is a Phase 2 study designed to evaluate the safety and efficacy of ABT-384 in approximately 260 adults with mild-to-moderate Alzheimer's Disease (AD). Subjects will be randomized to one of four treatment groups (ABT-384, donepezil, or placebo) for a 12-week Treatment Period.

Inclusion Criteria:

1. The subject and caregiver must voluntarily sign and date and informed consent. If the subject is not fully competent, full informed consent must be obtained from a legal representative and assent must be obtained from the subject.
2. Subject is male or female between the ages of 55 and 90 years of age, inclusive, at Day-1.
3. Subject meets the NINCDS/ADRDA criteria for probable AD.
4. Subject has a Mini-Mental Status Examination (MMSE) score of 10 to 24, inclusive, at Screening Visit 1.
5. Subject has a Cornell Scale for Depression in Dementia (CSDD) score ≤ 10 at Screening Visit 1.
6. With the exception of a diagnosis of mild-to-moderate AD and the presence of stable medical conditions, the subject is generally in good health based on medical history, physical examination, vital signs, clinical lab tests and 12-lead ECG.
7. If female, subject must be postmenopausal for at least 2 years or surgically sterile.
8. If male, the subject is surgically sterile (vasectomy), is sexually inactive, or is using a barrier method of birth control.
9. Subject has an identified reliable, caregiver (e.g., family member, social worker, nurse), who will provide support and ensure compliance with the study medication and procedures.
10. Subject and caregiver are fluent in the language used for administration of the rating scales or cognitive tests and have sufficient visual, hearing and graphomotor skills to complete procedures.

Exclusion Criteria:

1. Subject has a known hypersensitivity or intolerance to donepezil that led to discontinuation or a known reported history of donepezil treatment failure.
2. Subject is currently taking or has taken a medication for the treatment of AD or dementia within 60 days of Screening Visit 1, or is participating in cognitive therapy for the treatment of AD or dementia.
3. Subject has a history of a drug or alcohol disorder (abuse/dependence), based on either DSM-IV-TR or ICD-10 criteria, excluding nicotine, within 2 years prior to Screening Visit 1.
4. In the opinion of the investigator, the subject has any clinically significant uncontrolled medical or psychiatric illness that would affect the safety of the subject.
5. The subject has a current thyroid disease or history of thyroid disease, and is not currently being treated with a stable dose of thyroid replacement medication.
6. For any reason the investigator considers the subject to be an unsuitable candidate to receive ABT-384 or donepezil.