A host-specific toxin-related compound, HV-toxin M, was isolated from a culture medium of the phytopathogenic fungus, Helminthosporium victoriae, a causal agent of Victoria blight disease of oat. The structures of six amino acid components of HV-toxin M have already been determined in Part I in this series. In this report, Part II, the sequence of these six amino acid components is clarified by analyzing the results of FAB-MS/MS (fast atom bombardment-mass spectrometry/mass spectrometry: tandem mass spectrometry), a recent MS technique, on MS fragments of Toxin M or its derivatives (Fig. 1). This also gave strong support to the already proposed amino acid sequence in victorin C by the newer technique, as has already been reported in a preliminary report.7) In this paper, we describe details of the structural assignments of Toxin M (I in Fig. 1).