Reverse genetic studies in zebrafish, Danio rerio, have been carried out with morpholino phosphorodiamidate (MO) oligonucleotide injections into fertilized zebrafish embryos. While generally effective, not all injected MOs efficiently inhibit translation and in some cases nonspecific mistargeting effects are observed. We are studying alternatives to the MO derivative that could improve specificity and potentially lower cost. One such derivative, negatively charged peptide nucleic acids (PNA), exhibited comparable potency and greater specificity in targeting four different zebrafish developmental genes. We will pursue this new derivative for reverse genetic studies of uncharacterized zebrafish genes, especially homologs of mammalian oncogenes.