The EORTC Breast Cancer Cooperative Group carried out a randomized trial to compare doxorubicin with epirubicin as second-line chemotherapy in patients with metastatic breast cancer. Two hundred and fifty-nine patients with at least one site of metastatic disease entered this trial, of whom 232 patients were eligible. Treatment consisted of doxorubicin 75 mg m(-2) or epirubicin 90 mg m(-2) i.v. every 3 weeks. The overall response rates for doxorubicin and epirubicin were 36% and 28% respectively (P = 0.173). The median time to progression was 23 weeks for doxorubicin and 19 weeks for epirubicin (P = 0.063) and the median duration of response was 40 weeks for doxorubicin and 32 weeks for epirubicin (P = 0.059). The median survival was 47 weeks for doxorubicin and 44 weeks for epirubicin (P = 0.196). Leucocyte count on retreatment day (P = 0.011) and platelet nadir (P = 0.031) were significantly lower in the doxorubicin-treated group. Also mucositis (P < 0.001), diarrhoea (P = 0.005) and haemorrhage (P = 0.048) were significantly worse in the doxorubicin arm. Nine patients on doxorubicin and two patients on epirubicin experienced congestive heart failure (CHF). At the dose levels used in this study, no statistical differences in response rate and survival were found between the two treatment arms. Treatment with doxorubicin tended to result in a slightly longer duration of response and time to progression but doxorubicin was more toxic than epirubicin.