Childhood immunization programs may provide infrastructure for delivering vitamin A supplements to infants in developing countries. The effect of giving vitamin A, an immune enhancer, on antibody responses to trivalent oral poliovirus vaccine (TOPV) is unknown. A randomized, double-blind, placebo-controlled clinical trial was conducted to determine the effect of giving vitamin A simultaneously with TOPV on antibody responses to poliovirus. Infants (n = 467) received oral vitamin A, 15 mg retinol equivalent (RE), 7.5 mg RE or placebo with TOPV at 6, 10 and 14 wk of age. Antibody responses to poliovirus types 1, 2 and 3 were measured by a microvirus neutralization assay at enrollment and at 9 mo of age. Seroconversion rates to poliovirus types 1, 2 and 3 ranged from 98 to 100% in the three treatment groups, and there were no differences in mean antibody titers to poliovirus types 1, 2 and 3 among treatment groups. This study demonstrates that oral vitamin A does not affect antibody responses to poliovirus vaccine when integrated with the Expanded Program on Immunization.