Using energy minimization techniques previously described, the structure of gramicidin S proposed by Hodgkin and Oughton and by Schwyzer was taken as a starting point for the minimization procedure.After energy minimization, the resulting structure differed from the initial one, and had an energywhich was con siderably lower than that of any structure of gramicidin S heretofore reported. However, like the Hodgkin- Oughton-Schwyzer structure from which it was derived, it is consistent with the chemical evidence. © 1969, American Chemical Society. All rights reserved.