The following markers of inflammation: enzymatic activity of leukocyte elastase (LE), functional activity of alpha-1-proteinase inhibitor (α1-PI), levels of C-reactive protein (CRP) and interleukin-6 (IL-6) were measured in the blood plasma of patients with Alzheimer's disease (AD) and vascular dementia (VD). The results confirm the presence of an inflammatory component in the pathogenesis of AD and VD. The high level of CRP may be considered as a marker of VD in the early stages of disease. There was an elevation of α1-PI activity in AD patients compared to age-matched controls. The α1-PI activity, levels of CRP and IL-6 increased with the severity of dementia while the LE activity significantly decreased compared to controls (p<0.01). In patients with AD, the IL-6 level was negatively correlated with MMSE scores (Spearman r = -0.46, p=0.0077) and, therefore, can be considered as a biological marker of the severity of the pathological process. Positive correlations between CRP and IL-6 may plausibly reflect an ability of IL-6 to induce the synthesis of CRP.