A study was made of the effect of autopsy brain extracts from persons with dementias of different origin (Alzheimer's disease and senile dementia) on nervous tissue culture of human fetuses. Light microscopy showed a tendency towards an increase of the astrocyte count and expressivity of their immunocytochemical response to glial fibrillar acid protein after administration of brain extract from persons with Alzheimer's disease. Electron microscopy revealed a substantial rise of the frequency of occurrence of altered microtubules in the processes of ectodermal cells, particularly marked due to the effect of extracts from persons with senile dementia. It was also shown that cytoplasm of hypertrophied astrocytes was loaded with regulated bundles of +glial filaments (primarily in experimental culture series). Brain extracts from persons with Alzheimer's disease induced as well the formation of typical complexes in the synaptic structures.