<jats:p><jats:bold>Lantibiotics are peptide antibiotics which contain lanthionine.</jats:bold> Pep 5, a strongly basic compound, is produced from <jats:italic>Staphylococcus epidermidis 5</jats:italic> by ribosomal synthesis of a precursor peptide and post‐translational modification. The antibiotic activity of Pep 5 rests on the formation of strain‐dependent pores in bacterial membranes. Pep 5 is the hitherto largest lantibiotic (<jats:italic>M</jats:italic><jats:sub>r</jats:sub> = 3488). It is <jats:italic>N</jats:italic>‐terminally blocked by a 2‐oxobutyryl residue and contains, besides 25 protein amino acids, dehydrobutyrine (2), <jats:italic>meso</jats:italic>‐lanthionine (2) and 3‐methyllanthionine (1). Automatic Edman degradation, mass spectrometry of enzymatically obtained fragments and chemical derivatization gave a 34‐peptide sequence with three sulfide rings (lanthionine = S(CH<jats:sub>2</jats:sub>CHNH<jats:sub>2</jats:sub>COOH)<jats:sub>2</jats:sub>).