Twenty-six patients with advanced breast cancer were treated with a new anti-estrogen, Droloxifene (3-hydroxy-tamoxifen). They had all used tamoxifen either in the adjuvant or the advanced situation. The dose schedule was 100 mg orally daily. Partial remissions were observed in 4 (15%) of the patients, and in another 5 patients stable disease (greater than 24 weeks of duration) was observed. Three of the responders were resistant to tamoxifen. Fourteen of the 26 patients had no side-effect. In 2 patients therapy had to be stopped due to fatigue. Droloxifene seems to be an interesting new anti-estrogen which should be further exploited.