One hundred five patients with Stage III or IV epithelial ovarian cancer whose disease had persisted or recurred after primary surgery and first-line chemotherapy were given tamoxifen (20 mg orally twice daily) and evaluated for response. Eighteen percent of the patients responded: 10% demonstrated a complete response (CR) and 8% showed a partial response (PR). Thirty-eight percent of the patients had short-term disease stabilization. CR had a median duration of 7.5 months, with the longest lasting 17 months. For patients with PR or stable disease, the median duration of response was 3 months (maximum duration, 9 months). When estrogen receptors of tumor tissue from patients demonstrating CR were evaluated, eight of nine (89%) had elevated estrogen receptor levels. This contrasts with patients who had stable or progressive disease as only 59% of them had measurable estrogen receptors (P = 0.16).