The antibacterial peptide, magainin 2, from frog skin is known to be effective on a wide spectrum of microbial and fungal life. However, it has not been tested as a transgene which could confer disease resistance in aquatic organisms. We tested the expression of a magainin gene construct in zebrafish embryos and fry using reverse-transcription PCR and inhibition zone assay. Magainin 2 mRNA was detected in 5, 10, 24, and 48 hr embryos and 5-day and 15-day fry. Inhibition assay indicated that it was effective on membrane defective E. coli strains, but not the wild types. The usefulness of magainin as antibacterial peptide in conferring disease resistance is discussed.