Peptaibols are membrane-active polypeptides isolated from fungal sources. They are characterized by the presence of an unusual amino acid, alpha-aminoisobutyric acid, and a C-terminal hydroxylated amino acid. Peptaibols exhibit antibiotic activity against bacteria and fungi. Their amphipathic nature allows them to self-associate into oligomeric ion-channel assemblies which span the width of lipid bilayer membranes. Over 200 peptaibol sequences have been reported to date, which are compiled in the Peptaibol Database at http://www.cryst.bbk.ac.uk/peptaibol. Alignments of these sequences have been carried out in order to define a series of related subfamilies (SFs) with common sequence features thought to be important for channel formation. Crystal structures determined for a number of peptaibols from the various SFs provide the bases both for modelling of the channel structures and for modelling structures of other members of the same SFs.