Serum and cerebrospinal fluid (CSF) from 44 patients with clinical probable Alzheimer's disease (AD) (subdivided in two groups with 18 early onset, EO, and 26 late onset, LO, cases), 10 patients with vascular dementia (VD) and 24 patients with major depression (MD) were assayed for concentrations of albumin and IgG. The severity of dementia was assessed with the Mini Mental State Examination. The CSF/serum ratio for albumin and IgG as well as the IgG index were used to evaluate blood-CSF barrier function. Various patients showed signs of blood-CSF-barrier (BCB) dysfunction and only few displayed evidence of local IgG synthesis in the central nervous system (CNS) in the AD, VD and in the MD group (IgG index > 0.7). The permeability of the blood-CSF barrier was not correlated to measures of dementia severity. Our data support the hypothesis of a BCB leakage in a subgroup of all investigated patients. Furthermore, we found a small number of patients with increased intrathecal IgG synthesis. Elevated CSF immunoglobulins combined with BCB impairment might be associated or caused by a general immune activation. Our data are in agreement with the assumption that an inflammatory process may play a role in a subgroup of patients with AD but also with MD and less likely in VD. In conclusion BCB impairment and elevated IgG immunoglobulin levels are unspecific either for AD, VD or MD.