To detect and quantitate hepatitis B virus (HBV) DNA, semi-nested polymerase chain reaction (PCR) method was designed for amplifying the HBV core region DNA. Cloned HBV core region DNA was used as a quantitation control, and upon electrophoresis of the semi-nested PCR product, one, two, or three bands of amplified DNA were observed using a small (< 50 mol), moderate (around 200 mol), or large (> or = 1250 mol) quantity of the template DNA, respectively. Using this semi-nested PCR method, HBV DNA was quantitated in donated blood and tested for HBV serological markers. Most of the HBV surface antigen (HBsAg) high titer samples showed three bands on the electrophoresis, indicating a high level of HBV DNA, while most of the HBsAg low titer samples showed one band, indicating a low level of HBV DNA. HBV DNA was detected in 7 out of 36 HBsAg-undetectable and anti-HBc-positive samples (19.4%) but all 7 showed one band, indicating a low level of HBV DNA. In almost all of the HBV e antigen-positive samples the HBsAg titer was high, and three bands were observed indicating a high level of HBV DNA.