The histicline-rich peptide H5WYG (GLFHAIAHFIHGGWHGLIHGWYG) was found to induce membrane fusion at physiologic pH in the presence of zinc chloride. in this study, we examined the ion selectivity of the interaction of Zn2+ with H5WYG. This investigation was conducted by using adsorption at air/water interface and mass spectrometry. We found that a peptide-metal complex is formed with Zn2+ ions. Electrospray ionisation-mass spectrometry (ESI-MS) reveals that the [H5WYG + Zn + 2H](4+), [H5WYG + Zn + H](3+) and [H5WYG + Zn](2+) ions, appearing by increasing the amount of Zn2+ equivalent, correspond to a monomolecular H5WYG-Zn2+ complex. Tandem mass spectrometry (MS/MS) provides evidence for the binding of the single Zn 2+ ion to the H-11 and H-19 and probably H-15 residues.