Thirteen patients with rapidly advancing recurrent epithelial ovarian cancers, in whom chemotherapy and, in some cases, radiation therapy failed, were treated with the estrogen antagonist tamoxifen. The presence of cytosol estrogen receptors, which have recently been identified in ovarian cancer specimens, was determined in the tumor from each patient prior to tamoxifen treatment. No complete responses were observed. One patient had a partial response and 4 patients had prolonged stabilization of disease. All patients with stabilized disease had estrogen receptor levels that were borderline or high. Eight patients demonstrated no response to oral tamoxifen therapy, but 5 of these had partial small bowel obstruction secondary to advanced recurrent cancer. As tamoxifen in this preliminary study may have stabilized rapidly advancing recurrent ovarian cancer in combination with cytotoxic chemotherapy should be considered.