Our objective was to determine the immunologic response to two influenza vaccine doses in 39 children who had undergone liver transplantation. Patients received two doses of trivalent inactivated influenza vaccine 4 weeks apart. Sera were collected 4 weeks after each dose and analyzed by a hemagglutination inhibition assay (HAI) for evidence of antibody response to the antigens A/Taiwan/1/86 (H1N1), A/Beijing/32/92 (H3N2), and B/Panama/45/95. Patients with HAI titers of 1:40 or greater were considered to have protective titers. Twenty-six (67%) patients showed a 1:40 or greater titer response to A/Beijing/32/92 1 month after the first vaccination. Only two additional patients were found to have similar titers after the second dose. A higher proportion of patients with protective titers were on smaller amounts of prednisone for body weight or alternate day low dose (< 10 mg/day) prednisone compared to patients on daily low dose or daily high dose prednisone. Patients with protective titers were significantly older (9.0 +/- 2.8 years) than those without protective titers (4.2 +/- 3.4 years, p = .002) following the first inoculation of the A/Beijing/32/92 vaccine component. Similar results were found for the second vaccination and with the H1N1 antigen. Cyclosporine level, gender, and body mass index were not associated with any outcome measures. We conclude that most liver transplant recipients had a protective antibody titer after a single influenza inoculation, but little further advantage was gained after an additional dose. Vaccination of household contacts of younger patients and those patients on daily prednisone or patient chemoprophylaxis may offer greater benefit in prevention of influenza in liver transplant recipients than multiple vaccine doses with current vaccine preparations.