Eighty-five fungi isolated from prepared feed and from corn collected on farms were grown separately in moist autoclaved corn. The corn was fed to virgin weanling rats for 5 to 12 days; the rats were then killed, and their uteri were removed and weighed. Twelve isolates of Fusarium from corn and one from poinsettias caused increases of five to eight times in weight of the uterus as compared with controls that were fed sound corn. The greatest increase in weight of the uterus was caused by corn inoculated with Fusarium No. 5 incubated for 21 days at 20 to 25 C followed by 14 days at 12 C. Extraction of this corn with methylene chloride, separation into fractions by means of a silicic acid column, and further purification by thin-layer chromatography yielded a compound with ultraviolet-absorption maxima at 314, 274, and 236 mmu.