A highly toxic principle produced by molds or fungi. One type, the aflatoxins, is produced by the Aspergillus flavus fungus; another is a member of the tricothecene group produced by the fusarium fungus. This has been identified in samples of the so-called “yellow rain” in Southeast Asia, where it is said to have been the cause of many deaths among war refugees. Its presence there is subject to some conjecture, since the fusarium fungus cannot germinate in the humid environment of that area. There is substantial evidence (blood tests, autopsies, and contaminated gas masks) that the former U.S.S.R. have used such lethal agents in Afghanistan also.