The invention relates to peptides with biological activity against infection having the amino acid sequence Z1-LE-X1-IP-X2-X3-X4-P-X5-X6-X7-X8-X9-X10-K-X11-X12-X13-X14-X15-Z2, wherein X1 is a lysine, alanine, or aspartic acid; X2 is a cysteine, methionine or isoleucine; X3 is a serine, cysteine, lysine or glycine; X4 is an isoleucine, alanine, phenylalanine or cysteine; X5 is a proline, D-proline or a substituted L- or D-proline; X6 is a cysteine or glutamic acid; X7 is an amino acid with a hydrophobic or an aromatic side chain or cysteine; X8 is an amino acid with a hydrophobic or an aromatic side chain or cysteine; X9 is an amino acid with an aromatic side chain; X10 is a glycine, alanine or asparagine; X11 is a proline, aspartic acid, octahydroindolyl-2-carboxylic acid or D-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid; X12 is a phenylalanine, alanine, glycine, glutamic acid or D-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid; X13 is an amino acid with a hydrophobic or an aromatic side chain; X14 is an amino acid with a hydrophobic or an aromatic side chain; X15 is a phenylalanine or deletion; Z1 is NH2 or a sequence of 1 to 10 amino acid residues; Z2 is COOH or a sequence of 1 to 10 amino acid residues; and peptides which are fragments and/or covalently linked oligomers and/or derivatives, especially amidated, alkylated, acylated, sulfated, pegylated, phosphorylated and/or glycosylated derivatives, and mutants thereof, and with the provisio that (a) if X12 is alanine, glycine, glutamic acid, or D-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid than X13, X14 and X15 are phenylalanine, valine and phenylalanine respectively; and/or (b) if X12 is phenylalanine, than X13, X14 and X15 are valine, phenylalanine and a deletion, respectively; and (c) that there are at maximum two cysteine residues in a peptide.