Sixty patients with metastatic or primary inoperable breast cancer not suitable for hormone alteration therapy were blindly randomized between weekly 5-fluorouracil, intravenously, and daily physiologic doses of conjugated estrogens by mouth against weekly 5-fluorouracil, intravenously, and placebo. There was no difference in the survival or the effect on the tumor in the two groups. Numerous factors were analyzed as to their effect on the course of the disease. The number of organ sites of tumor involvement, age of the host, and previous treatment for the disseminated disease were not shown to influence the survival or the results of therapy of either group. However, the duration of the clinical cancer-free period from primary treatment to recurrence, the sites of organ involvement, and the performance status of the patients at the time of entry into the study significantly did influence the survival. There is no evidence in this study that physiologic doses of conjugated estrogens deleteriously influenced the course of the disease.