AbstractThe crystal structures of the peptaibol antibiotics cephaibol A, cephaibol B and cephaibol C have been determined at ca. 0.9 Å resolution. All three adopt a helical conformation with a sharp bend (of about 55° ) at the central hydroxyproline. All isovalines were found to possess the D configuration, superposition of all four models (there are two independent molecules in the cephaibol B structure) shows that the N‐terminal helix is rigid and the C‐terminus is flexible. There are differences in the hydrogen bonding patterns for the three structures that crystallize in different space groups despite relatively similar unit cell dimensions, but only in the case of cephaibol C does the packing emulate the formation of a membrane channel believed to be important for their biological function. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd.