European Study of 3APS in Mild to Moderate Alzheimer's Disease Patients

RECRUITMENT OF PARTICIPANTS IS PERFORMED ONLY BY STUDY SITES. INCLUSION CRITERIA: Participants must meet the following inclusion criteria to be eligible. * Male or Female (age 50 years and older): Female must be of non-childbearing potential (i.e. surgically sterilized or at least 2 years post-menopausal). * Diagnosis of probable Alzheimer's disease based on the National Institute of Neurological and Communicative Disorders and Stroke/Alzheimer's Disease and Related Disorders Association (NINCDS-ADRDA criteria). * Severity of dementia of mild to moderate degree as assessed by the Mini Mental State Examination (MMSE) performed at the screening visit. * Patient must be living in the community with a reliable caregiver. Participant living in an assisted living facility may be included if study medication intake is supervised and participant has a reliable caregiver. * Potential participant must be treated with an acetylcholinesterase inhibitor (donepezil, galantamine or rivastigmine) and must be on stable dose for at least 4 months prior to the screening visit and during the entire study period. * Participants must not have taken memantine for at least 4 months prior to the commencement of screening. The use of memantine is prohibited during the course of the study. * Fluency (oral and written) in the language in which the standardized tests will be administered. * Signed informed consent from potential participant or legal representative and caregiver. EXCLUSION CRITERIA: Patients will not be eligible to participate in the study if they meet any of the following criteria: * Potential participant with any other cause of dementia. * Life expectancy less than 2 years. * Potential participant with a clinically significant and/or uncontrolled condition or other significant medical disease. * Previous use of anti-amyloid or vaccine treatment for Alzheimer's disease. * Use of an investigational drug within 30 days prior to the screening visit or during the entire study. * Previous exposure to 3APS. * Inability to swallow pills.