A method for quantitative standardization of the DNA hybridization assay for hepatitis B virus (HBV) DNA protein complex in serum is described. This method was used to determine the titer of HBV DNA in various groups of subjects with HB surface antigen (HBsAg) in order to ascertain its accuracy as an index of infectivity. The method's detection limit was 10(5) genome equivalents or 0.3 pg DNA per ml. Titers of 5 X 10(7) to 5 X 10(8) genome equivalents per ml were found to be typical for persistent massive viremia, which occurred more frequently in symptomatic (30 of 48) than in asymptomatic (24 of 72) carriers positive for HBe antigen (HBeAg). Moderate viremia (10(5)-5 X 10(7)) was usually found in patients eliminating the virus from the blood. Patients with resolving acute hepatitis B were frequently positive at the onset (18 of 26) with moderate titers, but became negative within several weeks. In 11 patients who developed chronic hepatitis B, titers increased until typical massive viremia was evident. Whereas healthy HBsAg carriers with anti-HBe always had negative genome titers (144 of 144), symptomatic carriers with anti-HBe often had moderate genome titers (9 of 30). It is recommended that genome titers be monitored in HBeAg-positive and in symptomatic anti-HBe positive virus carriers in order to distinguish between virus carriers with high (greater than 5 X 10(7)), moderate (10(5) -5 X 10(7)) and low (less than 10(5)) infectivity.