The hepadnaviral DNA genome is synthesized by a viral-encoded reverse transcriptase, but the nature of this protein(s) in vivo remains obscure. We have previously described studies in which activity gel assays identified multiple DNA polymerase (DNAp) activities associated with highly purified duck hepatitis B virus (DHBV) core particles. We now report that virions isolated from viremic sera are associated with DNA-dependent DNAp activities which are nearly identical to major DNAp activities detected with highly purified DHBV core particles. These results suggest that the virion-associated polymerases are the same as those which are detected with core particles and are likely to represent DHBV pol gene products involved in replication of the genome.