The detection of serum hepatitis B virus (HBV) DNA in 32 chronic HBsAg carriers was performed by spot hybridization technique using both biotinylated and radiolabeled probes, in order to compare their specificity and sensitivity. Our results show that both assays are specific since neither evidence of cross-hybridization between HBV DNA and sera from patients with chronic non-A, non-B (NANB) hepatitis was found, nor HBV DNA was detected both in patients with chronic anti-HBs/anti-HBc-positive hepatitis and in patients negative for all HBV markers. An agreement between the two assays was observed in 94% of the tested sera. Even though in 5 serum samples (6%) low levels of HBV DNA (0.1-1 pg/100 microliter) remained undetected using the biotin-labeled probe, the lower detection limit of the two assays (0.1 pg of HBV DNA) was the same using purified Dane particles as control. This study indicates that the enzymatic detection of HBV DNA is suitable for routine and rapid monitoring of HBV replication in both HBeAg- and anti-HBe-positive patients, as well as for a semiquantitative analysis of serum HBV DNA.