The mycotoxins reviewed in this section comprise a family of closely related sesquiterpenoids produced by various species of fungi such as Fusayium, Myrothecium, Trichoderma, Trichothecium, Stachybotrys, Cephalosporium and Verticimonosporium, and are classified as trichothecenes after the isolation of trichothecin, the first member of the group to be discovered. All of the naturally occurring mycotoxins contain an olefinic bond at C-9, 10 and an epoxy ring at C-12, 13, and therefore are designated as 12, 13-epoxy-trichothecenes. During the past 20 years, 41 kinds of trichothecene derivatives have been known to occur, and many chemically and biologically modified toxins have been reported. The authors classified them into 4 groups as shown in Fig. 1; type A (basic trichothecenes), type B (8-keto-trichothecenes), type C (bis-epoxides) and type D (macrocyclic trichothecenes). C-9, 10-dihydroderivatives such as dihydronivalenol were omitted from the figure.