A nonradioactive hybridization assay for the detection of hepatitis B virus (HBV) DNA in serum with a digoxigenin-labeled probe is described. The probe was sensitive, being able to detect 0.25 pg of homologous HBV DNA, equivalent to 7 x 10(4) genome copies. After extraction of DNA from clinical samples, the probe detected HBV DNA in 11 of 12 hepatitis B e antigen-positive sera and did not react with 6 hepatitis B surface antigen-negative sera. This result was comparable to that obtained with a radiolabeled probe. When serum samples were treated by the alkaline denaturation method, some false-positive reactions were apparent with the digoxigenin-labeled probe, although their frequency could be reduced to around 8% by modifying the sample treatment with a centrifugation step. Overall, the sensitivity and specificity of the digoxigenin-labeled probe indicate that it is a viable alternative to the radiolabeled probe for the detection of HBV DNA in serum. The lack of radioactive reagents in the digoxigenin labeling and detection system and its long shelf-life make this system suitable for routine use in laboratories.