Trichorzins PA are new members of the class of natural Aib-containing peptides, which are known under the common name peptaibols. They are produced by a Trichoderma harzianum strain and exhibit significant activity against mycoplasmas. From the natural peptide mixture, seven trichorzins PA (PA II and IV–IX) have been isolated by a procedure employing different chromatography steps and a final purification by reversed-phase HPLC. The amino acid sequence elucidation involved a combination of liquid secondary-ion mass spectrometry (LSIMS) and two-dimensional 1 H and 13C NMR spectroscopy. Trichorzins PA are 18-residue peptaibols which differ mainly from other, related peptides by the C-terminal amino alcohol which is either tryptophanol or phenylalaninol. They adopt a helical structure.