Using the highly sensitive Polymerase chain reaction (PCR) hepatitis B virus (HBV) DNA has already been detected in many patients negative for all other serological HBV markers [12]. But yet, the relevance of these findings as a marker of infectivity has not been determined. We therefore have used the PCR to examine the perinatal route of HBV transmission by testing sera from 109 mother-child pairs in Yaoundé, Cameroon. HBV-DNA was detected in 25 (23%) of the mother's sera from which only 5 were positive for HBsAg. At the age of 6 months only one baby out of 25 who could be retested had become positive for HBV-DNA, HBsAg, and HBeAg. Low serum HBV-DNA levels which are still detectable by the PCR therefore seem not to be associated with a high risk of perinatal HBV transmission.