<jats:p>Sporidesmin C has been isolated as its diacetate (C22H24ICN3O8S3) from the fungus Pithomyces chartarum and its structure assigned on the basis of chemical, N.M.R., and mass-spectrometric studies. The assigned structure corresponds to the cysteine analogue of sporidesmin with three sulphur atoms linked together in an unusual eight-membered ring.