The purpose of this study was to assess the serum antibody responses to both the hemagglutinin and the neuraminidase antigens of inactivated influenza vaccine in 45 elderly and 28 younger adults. After vaccination, antihemagglutinin antibody levels increased significantly and mean fold increases ranged from 2.8 to 22.0. Seroprotection rates were between 42.2 and 91.1% 1 month after vaccination and 15.6 and 84.4% 5 months afterward. Seroresponse rates ranged from 42.2 to 91.1% 1 month after vaccination and 15.6 to 82.2% 5 months afterward. After vaccination antineuraminidase antibody levels increased significantly and mean fold increases ranged from 3.6 to 12.3. Significantly higher antibody responses to both hemagglutinin and neuraminidase were observed for antigen A(H3N2) than for antigens A(H1N1) and B. In most instances there were no statistically significant differences between the elderly and the control subjects. Influenza vaccine was immunogenic in the institutionalized elderly, who developed good antibody responses to influenza hemagglutinin and neuraminidase antigens.