Hepatitis B virus (HBV) was first detected as the potential agent of hepatitis B with the aid of electron microscopy by David Dane in 1970. Today, a sensitive polymerase chain reaction (PCR) technique for the DNA encapsidated within this virus would be sufficient to detect HBV infections during the incubation period, the acute phase, and the recovery phase. In many cases, HBV DNA persists at low levels even after complete recovery despite cellular immunity and the presence of anti-HBs.