Antigenic variants of A/Texas/77 (H3N2) virus were selected in vitro using monoclonal antibody to virus haemagglutinin (HA). The antigenic variants and parental A/Texas/77 viruses were used to evaluate the frequency of anti-HA antibodies in the sera of children and adults using single-radial-haemolysis (SRH) tests. Twenty to 41 % of selected sera from adults, which contained antibody to the parental A/Texas/77 virus, failed to react with the different antigenic mutant viruses. A higher proportion of sera from children (37–58%) failed to react with the antigenic variants. Certain human sera and particularly those of children would appear to possess a more limited antibody repertoire to influenza HA, potentially allowing new antigenic variants to escape neutralization and spread in the community.