This is a Safety and Tolerability Study Evaluating a New Treatment for Subjects With Mild to Moderate Alzheimer's Disease.

• Adverse Events [ Time Frame: Assessments up through 28 weeks ] [ Designated as safety issue: Yes ]
  Monitor each subject for clinical and laboratory evidence of adverse events on a routine basis throughout the study
• Laboratory Data [ Time Frame: Assessments up through 28 weeks ] [ Designated as safety issue: Yes ]
  Assessments include hematology, clinical chemistry, urinalysis and urine drug/alcohol screens.
• Vital Signs [ Time Frame: Assessments up through 28 weeks ] [ Designated as safety issue: Yes ]
  Assessments include pulse, blood pressure and oral body temperature
• Physical examinations [ Time Frame: Assessments up through 28 weeks ] [ Designated as safety issue: Yes ]
  An examination of bodily functions and physical condition
• Brief Neurological examination [ Time Frame: Assessments up through 28 weeks ] [ Designated as safety issue: Yes ]
  Assessments include cranial nerves, motor and sensory system, reflexes, coordination, gait and station
• Brief Psychiatric assessments [ Time Frame: Assessments up through 28 weeks ] [ Designated as safety issue: Yes ]
  Assessments include mood, anxiety, psychosis or delusions, agitation, homicidal thoughts or behaviors.
• Columbia-Suicide Severity Rating Scale [ Time Frame: Assessments up through 28 weeks ] [ Designated as safety issue: Yes ]
  The scale is designed to assess suicidal behavior and ideation
• Cornell Scale for Depression in Dementia [ Time Frame: Assessments up through 28 weeks ] [ Designated as safety issue: Yes ]
  Assesses the signs and symptoms of major depression in patients with dementia.
• Electrocardiogram [ Time Frame: Assessments up through 28 weeks ] [ Designated as safety issue: Yes ]
  Measurements include heart rate, RR interval, PR interval, QRS duration and QT intervals

This is a long term extension study to evaluate safety and tolerability of subjects who complete study M10-985 which is evaluating a new treatment for subjects with mild to moderate Alzheimer's disease.

This is a Phase 2, open-label, multicenter, 28 week extension study to evaluate the long-term safety and tolerability of ABT-126 in subjects who complete dosing through Week 24 of Study M10-985. Up to 410 subjects may participate at approximately 30 sites in several countries.

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 was randomized into Study M10-985 and completed dosing through Week 24 in that study.
• With the exception of a diagnosis of mild to moderate AD 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 ECG.
• If male, the subject is surgically sterile (vasectomy, is sexually inactive, or is using a barrier method of birth control (condom) with spermicidal foam/gel/film/cream/suppository for the duration of the study and for 30 days following the last dose of study drug. However, if the male subject's partner has been postmenopausal for at least 2 years or is surgically sterile, then use of a barrier method of birth control is not required.
• 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.
• The subject and caregiver must have sufficient visual, hearing and graphomotor skills to complete the study procedures.

Exclusion Criteria:

• Experienced an adverse event or abnormal finding in physical examination, vital signs, laboratory profile and/or ECG measurements in Study M10-985 that indicates the subject could become medically unstable during the current study.
• The subject is currently taking or is expected to be prescribed any excluded medications (including acetylcholinesterase inhibitors or memantine), without the approval of Abbott medical monitor.
• The subject anticipates a move outside the geographic area of the investigative site or is planning extended travel inconsistent with the recommended visit intervals.
• The subject is currently enrolled in, or plans to participate in, another experimental study during the course of this trial.
• The subject developed any significant medical or psychiatric condition that, in the opinion of the investigator, renders the subject an unsuitable candidate to participate in this study.
• For any other reason the investigator considers the subject to be an unsuitable candidate to receive ABT-126 or to participate in this study.