Aims/Methods: To investigate the influence of transplacental hepatitis B core antibody (anti-HBc) on perinatal hepatitis B virus (HBV) transmission, we studied the anti-HBc titers in 294 mother-neonate pairs, Results: The anti-HBc titer was highest (10(5.13+/-0.80) to 10(4.36+/-0.97) in mothers, 10(5.13+/-0.76) to 10(5.5+/-0.98) in infants) in the 200 hepatitis B e antigen (HBeAg) positive hepatitis B surface antigen (HBsAg) carrier mothers and their infants, second highest (10(4.51+/-0.76) and 10(4.68+/-0.76)) in the 60 HBeAg-negative HBsAg carrier mothers and their infants, and lowest (10(3.11+/-0.76) and 10(3.24+/-0.83)) in the 34 non-carrier mothers and their infants (p<0.05). One hundred and ninety-two infants of HBeAg-positive carrier mothers received hepatitis B immunoglobulin as well as hepatitis B vaccines, and were followed prospectively from birth, Ten infants became HBsAg carriers, and their mothers had significantly lower anti-HBc titers than those of the mothers of 182 infants who did not become carriers (p=0.003), while maternal serum hepatitis B virus DNA levels (29.9+/-23.6 versus 39.9+/-58.1 pg/10 ml) did not differ in those two groups (p>0.25). The same was observed in the infants' anti-HBc titers in those two groups (p=0.0006). Conclusions: The association of lower anti-HBc titers in HBeAg-positive carrier mother-infant pairs and the development of carrier status in the infants suggests a positive role of anti-HBc in the modulation of mother-to-infant transmission of HBV. A high maternal anti-HBc level in serum may be a negative predictor of immunoprophylaxis failure in high-risk infants.