The structure of the phytotoxin syringomycin produced by a sugar cane isolate of Pseudomonas syringae pv. syringae was determined as & with NMR and mass spectrometry.Syringomycins are phytotoxins produced by the phytopathogenic bacterium, Pseudomonas svringae pv. syringae and show wide antimicrobial activity. The toxins are thought to be virulence determinants, but their structures have been uncertain for about two decades.ly2) Recently, Segre _ et _ al. proposed the structure of syringomycin E, the major component of a mixture of these toxins, as 2. 334) In our research for the phytotoxins produced by - P. syringae pv. syringae, we found that one strain of this bacterium produced new toxins named syringostatins, 5) and the structure of syringostatins were established as 2.6) The structures 2 for syringomycin E3s4) and the structures of syringostatins (z)6) are closely related. Besides the replacement of several amino acids, 2_ differs from 2 in two other major ways: the arrangement of the C-terminal two amino acids and the linkage of f3-hydroxyaspartic acid residue. In recent investigation, we found that P_ svringae pv. syringae SCI, isolated from sugar cane in Japan, produced syringomycins. In this communication, we report the isolation and the structural determination of the major syringomycin of this isolate. The structure differs slightly from that of syringomycin E reported by Segre g ,1.3v4