These data clearly show the sensitivity differences and the correlations between the HBV DNA and the DNA polymerase assay. The Abbott HBV DNA is a molecular hybridization test in a liquid phase using a 125I-labelled probe and allowing the detection and the quantitation of HBV DNA in serum samples. This test was found to be 20-200 times more sensitive than the DNA polymerase assay and its sensitivity was evaluated to be about 0.3 pg HBV DNA. It is very easy to use and the results are obtained within 24 hours. In the patients with persistent HBV infection a close correlation between the positivity of the DNA polymerase activity and of the HBV DNA (R = 0.94) was observed. These two markers evolve quite parallel whatever the results obtained in the HBe system or whatever the sample time in a group of patients treated with recombinant interferon.