A highly sensitive polymerase chain reaction (PCR)-based diagnostic assay was developed to detect the presence of hepatitis B virus (HBV) in human serum. The assay involved amplification of HBV DNA sequences using primers specific to HBV. This in vitro enzymatic amplification technique, when used in combination with molecular hybridization assay can detect HBV genome in the patient's serum, with a higher degree of sensitivity than achieved with dot blot assay. The assay can identify samples containing 3-10 virus particles.