An essential role for zinc in development of the fetal immune system has been documented. However, the effect of antenatal zinc supplementation on infants' postnatal immune response to vaccinations is unknown. The objective of this study was to evaluate the effect of zinc supplementation during pregnancy on immune response to the Bacillus Calmette-Guerin (BCG) vaccine and the Haemophilus influenzae type b (Hib) component of the combined diphtheria, tetanus toxoid and pertussis (DTP)-Haemophilus influenzae type-b (Hib)- conjugate vaccine in poor Bangladeshi infants. We immunized 405 infants whose mothers were supplemented daily with 30 mg elemental zinc or placebo beginning at 12-16 weeks gestation with the standard BCG vaccine at birth. A subcohort of 203 infants were in addition immunized at 1-month intervals with three doses of DTP-Hib vaccine starting at 9 weeks of age. The delayed hypersensitivity (PPD) skin test was performed in 345 infants at 24 weeks of age. Hib polysaccharide (PRP) antibodies were assessed for 91 infants at 4 and 24 weeks of age. In infants born with low birth weight (LBW) a lower proportion of negative responses to PPD skin test were observed in the zinc (66.2%) compared to placebo (78.5%) group (p = 0.07). No differences were observed in normal birth weight infants. There were no differences in proportion of infants above the protective thresholds for anti-PRP antibodies between zinc (81%) and placebo (89%) group. Geometric mean PRP antibody titres at 4 and 24 weeks of age were not different between groups. Zinc supplementation during pregnancy did not enhance immune response to Hib-conjugate vaccine but there was a suggestion of improved delayed hypersensitivity immune responses to BCG-vaccine in Bangladeshi LBW infants.