The main limitation in the application of therapeutic peptides is their rapid degradation by proteolytic enzymes. Thioether-bridges in peptides confer strong resistance against proteolytic degradation, can modulate receptor interaction and extend delivery possibilities. Their enzymatic introduction is chemo-, regionand stereo-specific and allows the stabilization of medically and economically highly important therapeutic peptides. This emerging technology has huge potential for the development of a large number of novel highly effective peptide drugs.