The in vivo infectivity titration of hepatitis B virus (HBV) has been biologically standardized in terms of chimpanzee infectious dose (CID50). The polymerase chain reaction (PCR) was used for in vitro enzymatic amplification of HBV DNA and comparison with CID50. Serial dilutions of human serum specimens containing HBV adw (CID50 10(-7] and ayw (CID50 10(-7.5] were tested to determine the reproducibility and sensitivity of PCR for the detection of HBV DNA. The detection limit of HBV DNA in serum using PCR was 10(-8) for either amplification of HBV DNA extracted from serum or direct amplification of HBV DNA in proteolyzed serum. The amplification efficiency of PCR in proteolysates was not significantly reduced by using a 0.25% concentration (vol/vol) of nonionic detergents and 2.5% concentration (vol/vol) of digested human serum. Thus, PCR is a specific and rapid method for in vitro detection of HBV DNA that is more sensitive than the in vivo infectivity titration of HBV by chimpanzee inoculation. Therefore, if HBV-related DNA cannot be detected by PCR in specimens or biologic products, they probably do not contain infectious HBV.