The partially purified and concentrated 500-600-folds protein fraction has been obtained from human brain extract. This protein fraction was used for the immunization of rabbits. The corresponding anti-sera have the potency to detect the brain specific alpha 1-globulin, which is not identical to known cytoplasmatic brain specific protein. These antisera were used for the control of the antigen purification procedure which included ion-exchange, affinity and hydropho'ic chromatography, gel-filtration and isochromatofocusing. The antigen, purified to the homogeneity, has the electrophoretic mobility of the alpha 1-globulins, M(r) = 110-10 kD, and isoelectric point at pH 2.9-3.1.