Changes in neuroimmune parameters and cytokine production have been reported in patients with Alzheimer's disease, including increased levels of interleukin-1 (IL-1) and histamine in brain tissue, cerebrospinal fluid and serum. Specific neuroimmune reactions may be responsible in part for astrogliosis and neuronal death in particular circumstances. Since IL-1 and tumor necrosis factor (TNF) tend to act synergistically in physiological conditions and in some pathological processes, we have studied the concentration of TNF-alpha in patients with Alzheimer's disease (AD) or multi-infarct dementia (MID) and in age-matched control subjects (CS) in order to evaluate possible changes in the levels of this cytokine with potential influence on the pathogenesis of AD. Serum TNF-alpha levels were significantly lower in AD (2.5 +/- 1.25 pg/ml, p < 0.01) and MID (1.64 +/- 1.17 pg/ml, p < 0.001) than in CS (10.66 +/- 8.92 pg/ml). A negative correlation between serum TNF-alpha levels and age in AD was found (r = -0.645, p < 0.01); however, no significant correlations were detected between serum TNF-alpha levels and mental performance, cerebrovascular risk, heart rate and blood pressure in either AD or MID. In conclusion, there is a marked reduction in the concentration of serum TNF-alpha in both AD and MID which seems to be poorly related to cognitive dysfunction and/or neurovascular damage, probably reflecting an endogenous immune dysregulation and/or an inhibitory reactive process in demented patients.