Zervamicin is a 16-residue antibiotic peptide produced byEm. salmosynnemata.It belongs to a broad class of α-helical peptides which interact directly with the lipid bilayer. In our strategy to investigate the structure and dynamics of membrane-associated peptides we follow an approach based on site-specific isotope labelling and measurement by means of stable isotope sensitive techniques. We have accurately determined the exact postion of deuterium atoms at Gln-11 of the antibiotic zervamicin-IIB from the FAB collision-induced dissociation FAB-mass spectra of the sodium cationized molecules.