By using cell-free preparations of uteri obtained from immature BALB/c mice, it was demonstrated that zearalenone and zearalanol, Fusarium mycotoxins, inhibited [3H]estradiol-17 beta binding to specific sites in cytosol. Significant inhibition was noted from zearalenone at 4 x 10(-6) M and from zearalanol at 4 x 10(-7) M. Unlabeled mycotoxins (5 x 10(-6) M) incubated with intact uteri caused translocation of specific estrogen binding sites into nuclei that were exchangeable with [3H]estradiol-17 beta. Zearalanol was more effective in this regard than zearalenone. Ability of the mycotoxins to compete with estradiol-17 beta for the cytosol receptor and to cause translocation of the receptor to the nucleus in general is correlated with their biological activity. These data suggest that the uterotrophic effects of Fusarium mycotoxins are mediated through their association with estrogen receptors in the uterus.