The estrogenic effect of the ethylenebisdithiocarbamate fungicide Novozír MN 80 (Duslo, Sal') was studied by means of the screening method determining the reproductive risk of chemical substances, recommended by the Environmental Protection Agency. Compared to intact controls, a significant increase in relative uterine weight was recorded in the group of animals which received 1/25 of the maximal tolerable concentration of Novozír MN 80. Compared to negative controls (Tween 80), the relative uterine weight was increased significantly after administration of 1/25 and 1/50 of the maximal tolerable concentration of Novozír MN 80. On histologic examination the cuboidal epithelium of the mucous membrane was found to be changed into columnar epithelium, with uneven distribution of enlarged nuclei in the vacuolized cytoplasm. At 1/25 maximal tolerable concentration thickening of the uterine wall was observed.