Trichorzianine A IIIc is the main component of a peptide mixture isolated from a sporulated culture of Trichoderma harzianum that inhibits the growth of some fungal plant pathogens. This novel peptide has been shown to consit of one acetylated N-terminal residue, 18 amino acids, and a tryptophan01 C-terminal amino alcohol. Sequence assignment was based on positive-ion FAB mass spectrometry and high-field NMR data using two-dimensional NMR assignment techniques and proton NOE difference studies. Information on the conformation was derived from JNHX~H coupling constants, solvent and temperature NH chemical shift dependence, and transfer of solvent saturation experiments. These data show the N-terminal part of the peptide to be ordered in a helix, the first turn of which is of the 310 type.