Patulin and diacetoxyscirpenol are potent inhibitors of the sporulation of fungi, Aspergillus flavus, A. niger, Penicillium expansum, Neurospora crassa, Cladosporium herbarum, Rhizopus nigricans, Thamnidium elegans, and Mucor spinosus. The toxicity of diacetoxyscirpenol is markedly higher than that of patulin. The rate of spore production decreases with increasing toxin concentration and is totally suppressed by 100μg/filter disk. The phycomycetes tested are especially sensitive. Patulin suppresses the germination of the spores of Cladosporium herbarum, Rhizopus nigricans, and Thamnidium elegans almost completely in 100μg amount whereas diacetoxyscirpenol shows this effect only in the last mentioned fungus. Thamnidium elegans is very sensitive to all mycotoxins so far tested.