Injection of a single-strain vaccine evokes in the adult person an antibody-recall mechanism previously established by initial childhood antigenic experiences with related influenza viruses. This now bolsters antibody levels against viruses from that family of strains and provides some degree of protection against influenza caused by a new variant. To gain better understanding of age-related differences in antibody foundations in influenza immunization, groups of children and adults were given two different polyvalent influenza vaccines. The six-strain preparation (1,000 chick-cell-agglutination units) produced no greater incidence of undesirable side-effects than those obtained with the standard four-strain formula (500 CCA units) and repeatedly stimulated superior antibody responses. Children generally produced better antibody levels than did adults with use of the six-strain vaccine.