The known protective effects of passively acquired maternal antibody on the resistance of newborns to infections have prompted widespread interest in maternal vaccination. However, a range of animal model and human studies indicate potential inhibitory effects of maternal antibody on vaccine-specific humoral responses in infants. In the present study we have examined the relationship between maternally acquired TT-specific IgG present before DTaP vaccination and subsequent TT-specific T-cell memory responses at 12 and 18 months, in a cohort of 118 infants. We demonstrate a strong positive association between TT-specific cellular immunity as evidenced by increased IL-4, IL-5 and IL-13 responses, and maternal TT-specific IgG.