Samples of human serum gamma-globulin modified by equimolar binding of copper and zinc cations were obtained using the method of molecular ultrafiltration. Conformation characteristics of the protein were studied by UV spectrophotometry. Immunochemical study included radial immunodiffusion test, direct and sandwich enzyme immunoassays. Conformation changes in gamma-globulin caused by incorporation of solitary metal cations into the protein molecule modified presentation of antigenic determinants on the globule surface and their availability for recognition by specific antibodies. New antigenic determinants and new antigenic specificity of gamma-globulin are not formed under these conditions.