Zearalenone is an estrogen produced by Fusarium roseum as well as other species of Fusarium. We are studying the various derivatives of zearalenone produced by these isolates in nature as well as the other toxins associated with them when colonizing foodstuff. Zearalenone regulates the sexual stage in swine and rats as well as in the fungus that produced it. We are attempting to define the mode of action of this estrogen in both fungi and animals to determine if the mechanism is similar in both systems. Cyclic-AMP has been found to be associated with the sex-regulating activity in Fusarium, as in animals. Experiments will be conducted to determine if Fusarium also has an estrogen binding substance as found in animals. Other toxins produced by Fusarium and associated with zearalenone in nature are also being studied in order to more fully understand the entire syndrome (all the signs) reported in animals affected by this Fusarium-associated mycotoxicosis.