This study will investigate the ability of ST101 to improve memory in people with Alzheimer's disease who currently receive 10 mg Aricept® (donepezil) per day. This study also will examine the safety and tolerability of the drug. This study is evaluating 3 different dose levels of ST101 and placebo. Patients will have a 1 in 4 chance of getting placebo. All eligible subjects will be provided with bottles of 10 mg Aricept (donepezil) during the study drug administration part of the study.

Alzheimer's disease (AD) is a progressive and fatal neurological illness. It produces changes in the brain that include loss of cells and accumulation of abnormal protein deposits. Initial symptoms are cognitive, with deficiencies in short-term memory the most common symptom. As the disease progresses so does the severity of cognitive deficiency. Loss of speech and immobility occur in the terminal stages There is no cure for AD and no marketed treatment that modifies the underlying disease process. Available therapies improve some symptoms of AD by increasing brain concentrations of molecules involved in cognition. ST101 differs from marketed therapies in that it has demonstrated two actions in animal research testing. It improves cognition and it also reduces the accumulation of abnormal protein deposits in the brain. These two properties suggest that ST101 may be a promising agent for the treatment of AD. This study is designed as a preliminary dose exploration/proof-of¬concept investigation of the ability of ST101 to improve cognition during 12 weeks of administration.

Inclusion Criteria:

• Subjects must be receiving concurrent treatment with 10 mg/day of Aricept (donepezil). The dose shall have been stable for three (3) months (90 days) prior to Screening.
• Diagnostic evidence of Moderate to Moderately Severe Probable Alzheimer's disease
• CT or MRI results within the past 18 months that rule out dementia due to non-Alzheimer's etiology.
• A reliable and capable caregiver.

Exclusion Criteria:

• Subjects who reside in a skilled nursing facility.
• Subjects with B12 or folate deficiency.
• Subjects with chronic hepatic disease.
• Subjects with a recent history of hematologic/oncologic disorders.
• Subjects who have experienced a myocardial infarction with the past year.