The DNA-HBV was investigated in 109 serum samples from 75 patients with different forms of infection with the HB virus, using an RIA hybridization technique (Genostic-Abott). DNA-HBV was present in 12 of 18 cases of acute hepatitis, 1 of 3 patients with fulminant disease, 11 of 14 patients with chronic hepatitis and/or cirrhosis, 2 of 10 patients with hepatoma and 6 of 30 asymptomatic chronic carriers. Presence of DNA-HBV beyond 60 days in 7 patients with acute hepatitis established the chronic state. The highest levels were found in patients with chronic hepatitis or cirrhosis (mean 41 +/- 11 pg/ml) and the lowest in chronic carriers and patients with hepatoma. High levels of DNA-HBV denote persistent viral replication and would support antiviral treatment. Thus, investigation of DNA-HBV has diagnostic, prognostic and therapeutic implications in patients with Hepatitis B.