Erythrocytes modified to different extents with periodate were used in hemagglutination assays to investigate the binding properties of antihemagglutinin monoclonal antibody-selected antigenic variants of X-31 influenza virus. The results allowed differentiation of groups of variants and are discussed in relation to the nature of the amino acid substitutions in the variant hemagglutinins and their molecular locations relative to the receptor-binding site.
