Antiviral vaccines are needed for fish. 50 microg plasmid DNA in saline by the intramuscular route and 10 microg beta-gal protein in a commercial oil adjuvant by the peritoneal route induced serum antibody of the same titre and avidity in goldfish. The DNA expressed beta-gal under control of the immediate early promoter/enhancer gene of human cytomegalovirus. Commercial bacterin vaccines are administered to fish by the intraperitoneal route with oil and this route for DNA induced only 2-fold less antibody than DNA by the intramuscular route. Bacterin vaccines and antiviral plasmid DNA could therefore be co-injected into the peritoneum of fish in an oil adjuvant as a single dose.