New treatment methods for Alzheimer's disease (AD) have recently been tested, making early diagnosis more important. Therapy should be started during the initial stage of the disease in order to achieve the best outcome. This article presents activation paradigms obtained during the fMRI examination of patients with mild cognitive impairment (MCI), and the results of fMRI studies done in persons at increased risk of developing AD and during its early stage. The possibility of differentiating AD from other types of dementias and the influence of drug therapy on brain activation in AD patients is also discussed.