Influenza vaccination is less efficacious in adults older than 65 due to a decline in immune response with aging. It has been suggested that moderate exercise may aid in increasing the efficacy of the influenza vaccination in older individuals. In this study we evaluated the effect of moderate exercise on interferon-[Gamma] (IFN-[Gamma]) response to influenza vaccination in elderly adults over 65. Forty-eight sedentary elderly individuals were randomly distributed to either an aerobic exercise group or a control flexibility group. Subjects in the exercise group exercised at 65-80% heart rate reserve (HHR), 25-30 min, 3 days a week, for 18 months and the flexibility group performed low intensity flexibility/balance/resistance training during the intervention. All subjects received a trivalent influenza vaccine prior to the intervention and received an annual vaccination the following year. Blood samples were acquired at pre-immunization, 1, 4, and 12 weeks post-immunizations and IFN-[Gamma] levels were then measured in peripheral blood mononuclear cells (PBMC) after virus stimulation. HI antibody levels were also analyzed at pre, 1,4, 12, and 24 weeks post-immunization and correlated with IFN-[Gamma]. One year of exercise in elderly female subjects was associated with enhanced IFN-[Gamma] response to A/New Caledonia/99 (HINI) and B/Shanghai/2002 influenza antigen in PBMC cultured for 96 hours. A/Moscow/99, A/Fujian/2002, and B/Shanghi/2002 also stimulated PBMC collected pre and 1 week post-immunization to produce levels of IFN-[Gamma] that correlated with HI antibody production post influenza vaccination. In conclusion, one year of aerobic exercise in elderly females may help to enhance the efficacy of the influenza vaccination through enhanced stimulation of IFN-[Gamma] which may aid in predicting HI antibody levels to help protect against influenza infection.