The study is carried out in order to investigate if [11C]AZD2995, compared to [11C]AZD2184, is a more suitable PET ligand for in vivo imaging of β amyloid depositions in the human brain. In the study the two PET ligands will be examined in both healthy volunteers and patients with Alzheimer's Disease.

Inclusion Criteria:

• Alzheimer´s Disease patients - 50-85 years- mild to moderate AD, clinical progression of AD over 12 months.
• Healthy male volunteers: - Age 20-50 years, Body Mass Index: 18-30 kg/m2.
• Clinically normal physical findings including normal blood pressure and pulse rate.

Exclusion Criteria:

• Alzheimer´s Disease patients:
• significant cerebrovascular disease or depression, central nervous system infarct or infection or lesions
• clinically significant illness within 2 weeks before the study start.
• administration of any investigational product with effect on brain beta amyloid levels within 3 months prior to study and/or participation in a PET investigation other than study D0180C00011 as part of a scientific study during the past 12 months,.
• Healthy volunteers; - clinically significant illness within 2 weeks before the study start, history of psychiatric or somatic disease/condition that may interfere.- first degree relative with dementia. Obvious deterioration of memory functions.