From a group of 108 female patients with measurable and/or evaluable metastatic breast carcinoma, 52 were randomized to receive tamoxifen and 56 to receive tamoxifen and fluoxymesterone. The fluoxymesterone dose, given orally twice a day, was 7 mg/m2 body surface area. The tamoxifen dose per patient, also given orally twice a day, ranged from 2 to 100 mg/m2 body surface area. Eighty-five percent of the patients had received previous chemotherapy and 60% previous hormone therapy. The complete and partial remission rate was better with the tamoxifen and fluoxymesterone regimen (p = 0.016), with remission rates of 15% for tamoxifen alone and 38% for the combination. The tamoxifen and fluoxymesterone regimen appeared to have higher remission rates in all subsets of pretreatment variables. Duration of remission with each regimen was similar, but the overall time to treatment failure for tamoxifen and fluoxymesterone was longer than for tamoxifen alone (180 versus 64 days, p = 0.01). Median survival with the combination was 380 days compared to 330 days for tamoxifen. No significant dose-response relationships emerged. Side effects were not different between dose levels or regimens except for the androgen effects in the tamoxifen and fluoxymesterone combination. These results suggest that there is no major dose-response effect for doses ranging from 2 to 100 mg/m2 body surface area given twice daily in this largely (94%) postmenopausal pretreated patient group, and that the tamoxifen and fluoxymesterone regimen is superior to tamoxifen alone.