Alzheimer's disease (AD) is characterized by cognitive decline and loss of neurons in specific brain regions. Recent findings have suggested an involvement of brain-derived neurotrophic factor (BDNF) in the pathogenesis of AD. BDNF is an endogenous protein involved in the maintenance of neuronal function, synaptic plasticity and structural integrity in the adult brain. To our knowledge, the present pilot study assessed for the first time BDNF serum and CSF concentrations in 30 patients with different stages of AD in comparison to 10 age-matched non-demendet controls. AD patients were divided in two groups according to their MMSE score: Group 1 (n = 15) in early stages with MMSE scores >or=21 (mean of 25.5) and Group 2 (n = 15) with more severe stages of dementia with MMSE scores <21 (mean of 13.3). As main results, we found in patients with early stages of probable AD significantly increased BDNF serum concentrations as compared to more severe stages of AD (p < 0.0001) and age-matched healthy controls (p = 0.028). BDNF serum values in all AD patients correlated significantly with MMSE scores (r = 0.486; p < 0.0001). Levels of BDNF were below the detection limit of the assay in unconcentrated CSF samples of AD patients and non-demendet controls.In summary, BDNF serum values are increased in early stages of Alzheimer's disease, which may reflect a compensatory repair mechanism in early neurodegeneration and could also contribute to increased degradation of beta-amyloid (Abeta). During the course of the disease, BDNF is decreasing, which correlates with the severity of dementia. The decrease of BDNF may constitute a lack of trophic support with an increase of Abeta accumulation and thus contribute to progressive degeneration of specific regions in the AD-affected brain. BDNF should be further evaluated as a candidate marker for clinical diagnosis and therapeutic monitoring in Alzheimer's disease.