A new antigen was isolated from human tissue extracts. By immunofluorescence it was found only in granulocytic cells both in the cytoplasm and on the surface of these cells. It is an alpha-globulin having a molecular weight of approximately 47,000. It is unglycosylated and does not bind to various lectins. Due to its electrophoretic mobility and its cellular localization, it was named alpha-G (for granulocytes) globulin.