It has been proposed that some neonates infected with hepatitis B virus (HBV), acquire their infections in utero as demonstrated by HBV seromarkers in venous blood samples at birth. In this study, paired blood samples from 13 HBsAg-positive, 19 HBsAg- and HBeAg-positive, 2 HBsAg-negative mothers and 34 of their neonates, were drawn 24-72 hours after birth and tested for HBV-DNA in their peripheral blood mononuclear cells (PBMC). The presence of HBV-DNA in PBMC was detected in 69.2% (9/13) of HBsAg-positive mothers, 94.7% (18/19) of HBsAg- and HBeAg-positive mothers, and in none of their neonates. The conclusion from these results is that the evidence for hepatitis B infections occurring in neonates of hepatitis B carrier mothers in utero is uncommon.