The amino acid sequences of two closely related peptides from Gila monster (Heloderma suspectum) venom are reported. Helospectin I is a 38-residue peptide, His-Ser-Asp-Ala-Thr-Phe-Thr-Ala-Glu-Tyr-Ser-Lys-Leu-Leu-Ala-Lys-Leu-Ala- Leu-Gln - Lys-Tyr-Leu-Glu-Ser-Ile-Leu-Gly-Ser-Ser-Thr-Ser-Pro-Arg-Pro-Pro-Ser-Ser, and helospectin II is a 37-residue peptide identical to helospectin I except that it lacks serine 38. Helospectins are pancreatic secretagogues with structures and bioactivities similar to vasoactive intestinal peptide and other members of the glucagon superfamily. The relative significance of helospectin-I and helospectin-II is presently unknown. Comparison of the 28 residues of vasoactive intestinal peptide with residues 1-28 of helospectin shows that identical amino acids occur in 15 positions. Since members of the glucagon superfamily have similar structures but different biological actions, it is possible that helospectin is more closely related to a mammalian peptide awaiting discovery.