Abstract: There is provided peptide derivatives of the general formula ##STR1## wherein R.sup.1, R.sup.2 and R.sup.3 each represent the characterizing group of an .alpha.-amino acid of the type normally found in proteins; R.sup.4 represents a hydroxy or methyl group; n stands for zero, 1, 2 or 3; the configuration at the carbon atoms designated as (a), (b) and (c) is L (when R.sup.1 or R.sup.2 .noteq. H); and the configuration at the carbon atom designated as (d) is (R) (when R.sup.3 .noteq. H)and pharmaceutically acceptable salts thereof.The above compounds exhibit antibacterial activity against various microorganisms.