Evidence available indicates that the so-called Dane particles are the hepatitis virus. A DNA polymerase is associated with the core of these particles. The probability that this is the viral DNA polymerase offers the possibility of preventing hepatitis B multiplication by selective inhibition of this enzyme. This investigation reports that trisodium phosphonoformate (PFA) at low concentrations but not phosphonoacetate acid (PAA) inhitits Dane particle associated DNA polymerase.