With the use of the dot blot hybridization technic, sera from 30 consecutive patients with acute hepatitis B were examined for the presence of hepatitis B virus (HBV)-DNA. In an additional five patients with acute hepatitis B, serial serum samples, beginning before the serum alanine amino transferase elevation to the clearance of hepatitis B surface antigen, also were tested for various hepatitis B virus markers, including HBV-DNA. Thirteen of the 30 patients (43%) had circulating HBV-DNA and HBeAg at the time of their first clinic visit. However, 11 additional patients with HBeAg did not have HBV-DNA in their sera. In the 13 patients with HBV-DNA, there was no correlation between the titers of HBeAg and the levels of HBV-DNA. Examination of the serial serum samples from the additional five patients showed HBV-DNA and HBeAg to be present several days before the peak of serum alanine amino transferase. In all five patients, HBV-DNA was present in the serum before the appearance of IgM anti-HBc. However, HBsAg was present in all these patients' sera at the time of HBV-DNA positivity. None of the patients in this study became chronic carriers of hepatitis B virus.