The invention disclosed herein relates to the novel method for the preparation of cyclic peptides, wherein a linear peptide is reacted, in solution in a polar organic solvent, with an insoluble, resin-bound carboxyl-activating reagent such as resin-bound isopropylcarbodiimide. Cyclic peptides thus obtained have been found to retain biological activity characteristic of their linear counterparts, with increased biostability; the cyclic peptide, Gramicidin S, which can be prepared by this method, is a valuable antibacterial.