A DNA polymerase induced by Oncorhynchus masou virus (OMV) was isolated from cultured salmon cells infected with OMV using sequential ion-exchange column chromatography steps. The properties of the OMV polymerase were compared to those of human cytomegalovirus (HCMV) polymerase and polymerase alpha from cherry salmon (masu salmon, O. masou) testes. OMV polymerase was clearly distinguished from the other polymerases by its optimum temperature for enzyme activity, 25 degrees C. In an investigation of the effects of phosphonoacetic acid and aphidicolin, OMV polymerase was found to be more resistant to both drugs than HCMV polymerase.