The main ‘acute-phase proteins’ were determined in serum of 20 patients with presenile Alzheimer’s disease (AD) and compared with values in 18 age-matched healthy control subjects. Following parameters were evaluated: α1-antitrypsin (αAT), haptoglobin (HPT), transferrin (TRF), acidic α1-glycoprotein (A αG), ceruloplasmin (CER), α2-macroglobulin (αMG), C-reactive protein (CRP), albumin (ALB), together with the immunoglobulins IgG, IgM and IgA, and some of the most significant factors of the classic (C3, C4) and alternative (properdin factor B) pathways of complement activation. The results showed a statistically significant increase in the levels of aAT (p < 0.001), CER (p < 0.001) and of all the complement factors studied (p < 0.005). The levels of other acute-phase proteins (HPT, TRF, A αG, αMG, CRP, ALB) and immunoglobulins (IgG, IgM, IgA) were similar in AD patients and normal controls. These results give rise the possibility that these elements indicate an altered immunoregulation compatible with chronic cell damage and/or chronic inflammation conditions. Moreover, the increased level of αAT can be related to the low production of interleukin-1 (IL-1) reported in AD, which supports the hypothesis of a relative derangement of the macrophage function in preseni