In order to investigate the significance of HBV DNA in the serum of anti-HBs positive persons, the serum of 76 anti-HBs positive persons was studied for HBV DNA by means of polymerase chain reaction (PCR). The results showed that 21 (32.2%) out of 65 cases without hepatitis B vaccination were positive for HBV DNA detected with PCR (PCR-HBV DNA), but no one was positive for PCR-HBV DNA in 11 cases inoculated against hepatitis B. It was also found that 6 cases were positive for HBsAg-Ab immunocomplex in those positive for PCR-HBV DNA and the liver tissue in 2 of the 5 cases with liver-biopsy were positive for HBVAg determined with immunohistologic ABC method. We believed that persons, who acquired anti-HBs after HBV infection were different from those who were vaccinated, might carry HBV which come from the HBsAg-Ab immunocomplex and HBVAg positive hepatocytes. In addition, the study also proved that the PCR-HBV DNA positive rate correlated significantly with the anti-HBe and or anti-HBc positive rate and with the abnormal rate of liver function in the anti-HBs positive persons. It was suggested that persistent presence of HBV DNA in the bodies should be responsible for the persistent presence of anti-HBe and anti-HBc in the serum and also for the liver damage.