Gramicidin channels have been extensively studied for the last 10-15 years, and the basic channel structure and permeability characteristics are well understood. The relation between structure and function at the single-residue level and the detailed (or even not so detailed) understanding of ion movement through the channel is nonetheless still unavailable. This is, however, mainly a reflection of the level at which the questions are being asked. Gramicidin channels should continue to serve as general models for transmembrane channels, as their small size and experimental accessibility make them uniquely suitable to pursue biophysical investigations of general channel behavior. A particularly important feature of the gramicidin channels is the availability of total or semi-synthetic modifications of channel structure, which allows a freedom to modulate the molecule not available by genetic engineering methods. This should, in conjunction with molecular dynamics simulations, lead to a truly molecular understanding of the structure-function relation.