Doubt about the serologic efficacy of annually repeated influenza vaccination prompted investigations into the course of hemagglutination-inhibiting (HI), IgG, and IgA antibody titers and the IgG and IgA avidity index to influenza A/Taiwan/1/86 and A/Beijing/353/89 after annual vaccination. Fifty-four healthy elderly persons > 170 years of age and 24 healthy young adults < 30 years of age received standard influenza vaccine during 3 consecutive years. On average, prevaccination HI, IgG, and IgA titers to both influenza virus strains increased ≥4 fold between the first and the third vaccination (analysis of variance, P< .001). The postvaccination HI and IgG titers remained unchanged after annual vaccination. The avidity index of IgG and IgA antibodies increased somewhat after annual vaccination, although the increase was statistically significant only in the young subjects. These data indicate that annual influenza vaccination of healthy elderly and young subjects results in an overall increase in protective antibodies.