The present invention is directed to conotoxin peptides, specifically .delta.conotoxin PVIA and .mu.-conotoxin PIIIA. .delta.-conotoxin PVIA is found in the Eastern Pacific fish hunting species of cone snails Conus purpurascens. It consists of 29 amino acid residues of the sequence: Glu-Ala-Cys-Tyr-Ala-Xaa1-Gly-Thr-Phe-Cys-Gly-Ile-Lys-Xaa2-Gly-Leu-Cys-Cys-Ser-Glu-Phe-Cys-Leu-Pro-Gly-Val-Cys-Pro-Gly (SEQ ID NO:1) where Xaa1 or Xaa2 is Pro or 4-trans-hydroxyproline. The C-terminus may be free or amidated. .delta.-conotoxin PVIA is vertebrate specific and targets voltage-sensitive Na+ channels. .mu.conotoxin PIIIA is also found in Conus purpurascens. It consists of 22 amino acid residues of the sequence: Xaa1-Arg-Leu-Cys-Cys-Gly-Phe-Xaa2-Lys-Ser-Cys-Arg-Ser-Arg-Gln-Cys-Lys-Xaa2-His-Arg-Cys-Cys (SEQ ID NO:2) where Xaa1 represents pyroglutamate or glutamine and Xaa2 represents 4-trans-hydroxyproline or proline. This latter peptide targets sodium channels.
