F-19 NMR is a unique tool to examine the structure of fluorine-labeled peptides in their native cellular environment, due to an exquisite sensitivity and lack of natural abundance background. For solid-state NMR analysis, we isolated native membranes from erythrocyte ghosts and bacterial protoplasts and prepared them as macroscopically oriented samples. They showed a high purity and quality of alignment according to P-31 NMR, and the membrane-bound antimicrobial peptide PGLa could be detected by F-19 NMR. The characteristic fingerprint splitting of its F-19 reporter group indicated that the peptide helix binds to the native membranes in a surface alignment, albeit with a higher affinity in the prokaryotic than the eukaryotic system.