Women in the last trimester of pregnancy were given trivalent inactivated influenza virus vaccine (TIV; A/Sichuan/H3N2, A/Taiwan/H1N1, B/Victoria) or tetanus toxoid (TT). Maternal blood was drawn before immunization and at delivery (median, 5 weeks later); infant blood was obtained within 5 days of birth and 2 months later. Antibody responses to TIV and TT were determined by microneutralization assay and ELISA. T cell response was determined by lymphocyte proliferation. Maternal seroconversion to vaccine antigens was found to one or more influenza antigen in all TIV recipients and to TT in 9 of 13 TT recipients. Significantly higher IgG antibodies to maternal vaccine antigens were present in cord and infant serum. Significant blastogenic responses were seen to influenza A and Bin maternal cells ofTIV-immunized women but not in cord or infant lymphocytes. Maternal immunization resulted in higher infant levels of vaccine-specific IgG antibody but not in the transfer of specific T lymphocyte response(s) or production of neonatal IgM antibody.