The mycotoxin chlamydosporol (C11H14O5) has been independently isolated from three different Fusarium species (F. chlamydosporum, F. acuminatum and F. culmorum), suggesting that its distribution may be widespread. We have developed a sensitive, specific fluorometric assay for chlamydosporol that allows quantitation in crude culture extracts. Using this assay we have observed production of chlamydosporol on rice medium by 23 of 40 isolates (58%) of Fusarium sp. examined in amounts as high as 0.8% (wt/wt) dried culture medium.