Amyloid β42 (Aβ42) and proinflammatory cytokines such as interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) have been suggested to contribute to the pathogenesis of Alzheimer's disease (AD) and vascular dementia (VaD). Our aim was to examine whether the changes in these parameters would be able to discriminate the patients with AD from those with VaD and from healthy individuals. We have analyzed the levels of Aβ42, IL-6 and TNF-α in the serum of newly diagnosed 28 AD patients, 16 VaD patients and 26 healthy non-demented controls. We also investigated whether there is an association between Aβ42, IL-6 and TNF-α levels and mini-mental state examination (MMSE) scores and body mass indexes (BMI) of patients. Our data showed a significant decrease in serum Aβ-42 levels in AD patients compared to VaD patients and controls. Levels of IL-6 and TNF-α were not different between AD patients, VaD patients and controls. We observed a correlation between Aβ-42 levels and MMSE scores and BMI levels in both AD and VaD patients. However, Aβ-42 levels were not correlated with IL-6 and TNF-α levels. Significantly lower levels of Aβ42 found in the serum of AD patients than that of VaD patients and controls suggests that it can be a specific biochemical marker for AD.