This study will test two different doses of florbetapir F 18 to determine which dose is best to image amyloid plaques in the brains of Alzheimer's Disease (AD) patients using a positron emission tomography (PET) scanner.

Inclusion Criteria (AD group):

• Greater than 50 years of age
• Probable AD according to the National Institute of Neurological and Communication Disorders and Stroke-Alzheimer's Disease and Related Disorders Association (NINCDS-ADRDA) criteria
• Mild/moderate dementia as evidenced by a Mini-Mental State Examination (MMSE) score ranging from 10 to 24, boundaries included, at screening
• History of cognitive decline gradual in onset and progressive over a period of at least 6 months

Inclusion Criteria (healthy volunteer group):

• 35 to 55 years of age, inclusive
• MMSE of 29 or greater

Exclusion Criteria (both groups):

• Neurodegenerative disorders other than AD, including, but not limited to Parkinson's disease, Pick's disease, fronto-temporal dementia, Huntington's chorea, Down syndrome, Creutzfeldt-Jacob disease, normal pressure hydrocephalus, and progressive supranuclear palsy
• Diagnosis of other dementing / neurodegenerative disease
• Diagnosis of mixed dementia
• Cognitive impairment resulting from trauma, hypoxic damage, vitamin deficiency, brain infection, brain cancer, endocrine disease, or mental retardation
• Clinically significant infarct or possible multi-infarct dementia as defined by the NINCDS criteria
• Evidence on screening MRI or other biomarker that suggests alternate etiology for cognitive deficit (for healthy controls, evidence suggesting the presence of AD pathology)
• Clinically significant psychiatric disease
• History of epilepsy or convulsions
• Clinically significant hepatic, renal, pulmonary, metabolic, or endocrine disturbances
• Current clinically significant cardiovascular disease
• Received investigational medication within the last 30 days

AEs reported within 7 days of injection; SAEs reported within 30 days of injection.