To assess whether the administration of a booster dose of influenza vaccine may enhance immune response in hemodialysis patients, 58 subjects were given two doses of the 2003/2004 season influenza vaccine, 1 month apart. "European Agency for the Evaluation of Medicinal Products" (EMEA) criteria were fully met in terms of percentage of response and of mean-fold increase of hemagglutination inhibiting (HI) antibody titer, but not in terms of seroprotection rates (HI antibody titers > or =1:40). The second vaccine administration did not result in additional increase in seroprotection rate or in geometric mean titers. Protective immune response against the epidemic A/H3N2 Fujian-like strain, antigenically distant from that included in the vaccine (A/Panama/2007/99) was observed in 94.7% of vaccinees protected against the A/H3N2 vaccine strain 1 month after immunization. No adverse reactions were reported during follow-up. The study findings suggest that immune response to influenza vaccination may be suboptimal in hemodialysis patients and that the administration of an additional second dose of vaccine does not improve the humoral response.