In order to investigate the possibility of whether or not the lymphocytes of patients with Alzheimer's Disease (AD) are in an activated state, blood mononuclear cells from 45 AD patients and 45 healthy age matched controls were immunophenotyped by measuring the expression of CD3, CD4, CD7, CD8, CD25, CD28, CD56 and HLA-DR by flow cytometry. Circulating and in-vitro-produced cytokines were also measured by ELISA tests. CD7 and CD8 were significantly decreased in AD patients (48.3% and 18.2%, respectively) when compared to healthy subjects (63.2% and 28.3%, respectively). A significant increase in the CD4, CD25 and CD28 antigen expression was also observed in the AD group (55.3% 24.8% and 65.1%) with respect to healthy subjects (44.5%, 10.3% and 54.3%). In addition there was a significant difference in the extent of apoptosis in lymphocyte culture, as measured by mean fluorescence intensity (MFI) of Fas antigen (CD95) expression on CD4+ T cells in 6 AD patients (MFI = 36% and 43%, by anti-CD3 and hyperthermia mediated-apoptosis, respectively) with respect to 6 healthy individuals (MFI = 24% and 31%, by anti-CD3 and hyperthermia mediated-apoptosis, respectively), as well as in T-cell proliferation assay. A decline of Fas antigen expression on CD8+ subset was observed in the AD group with both stimuli (19% and 28%) comparing to the control group (29% and 39%). No differences were observed on circulating cytokines and spontaneous in vitro production of proinflammatory interleukin 1beta (IL-1beta), Tumor Necrosis Factor-alpha (TNF-alpha), IL-6 and IL-10 cytokines. Lipopolysaccharide (LPS)-stimulated in vitro production of IL-1beta, TNF-alpha, IL-6 and IL-10 measured by a whole blood culture system was significantly higher in AD patients comparing to controls. Furthermore, the observed differences were more evident at late stages of disease. These findings suggest that immunological tests, based on lymphocyte immunophenotyping combined with pro-inflammatory cytokine determinations and measurement of apoptosis in peripheral blood might represent a useful tool to obtain more insight into the pathogenesis of AD and into the level of immune activation which could characterize the pathological state of lymphocytes from individual AD patients.