Serum and cerebrospinal fluid (CSF) from 25 patients with dementia of Alzheimer type (DAT) and 25 controls were assayed for concentrations of albumin and IgG. The severity of dementia was rated 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 in the respective groups. The control group was matched for age, sex and the indirect alcohol parameters, mean corpuscular volume and gamma-glutamyltranspeptidase. There were no signs of dysfunction of the blood-CSF barrier for proteins or signs of local synthesis of IgG in the central nervous system (CNS) of the demented patients. The permeability of the blood-CSF barrier appeared to be unrelated to dementia severity. The data do not support the hypothesis that a pathological leakage through the blood-CSF barrier facilitates the entry of extraneuronal proteins to the CNS, which might contribute to the pathophysiological process in DAT.