Albumin and IgG have been determined in the serum and cerebrospinal fluid (CSF) of 64 patients affected by Alzheimer's disease and senile dementia of Alzheimer type (SDAT/AD), 17 multi-infarct dementia (MID) patients and 52 controls. The concentrations of albumin and IgG in the serum and CSF have been taken into account to evaluate the integrity of the blood-brain barrier (BBB) and the occurrence of intrathecal immunological activation in demented patients. Clear-cut signs of BBB damage have been shown only in the group of patients affected by MID, whilst none of the two groups of patients displayed signs of immunological activation, expressed by an increase in IgG index, nor abnormally low CSF/serum ratios for IgG, previously suggested as expressive of a "consumption" of IgG by the brain parenchyma.