Illudin M is a cytotoxic sesquiterpene from the fungus O. illudens that alkylates DNA. It is cytotoxic to HL-60 human leukemia cells at 6-100 nM. Illudin M was used as a base structure for the development of potential anticancer agents with less toxicity and improved efficacy. It is closely related to illudin S , which has been the focus of additional studies.