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1. A minimum of three distinct basic proteins have been chromatographically separated from a neutral, low ionic strength extract of human grey matter, using a discontinuous eluant series. 2. These chromatographic subfractions have been characterized by gradient elution chromatography and each subfraction analysed for distinct antigenic characteristics. 3. Evidence was adduced for the presence of a minimum of three distinct basic protein antigens, all of which may be specific to human brain but not to human liver. None of them appear to be human serum proteins.

1. Using chromatography on DEAE-cellulose, a neutral, low ionic strength extract of human grey matter has been separated into fractions of proteins with basic and progressively acidic groups. 2. The reactions of each group with rabbit antiserum against the original extract, in double-diffusion tests, suggest the presence of a minimum total of thirteen distinct antigens between them. These results are supported by immunoelectrophoretic findings, which indicate the basic group to contain five, and the progressively acidic group seven to eight distinct antigens. These antigens do not appear to be human serum proteins. 3. Antigens belonging to the BE class (resistant to boiling and relatively soluble in ethanol) are present among the progressively acidic proteins, and possibly among the basic proteins also.