The purpose of this study was to compare the activity and toxicity of epirubicin-vindesine (EV) with mitoxantrone-vindesine (MV) in patients with metastatic breast cancer. A total of 295 patients was randomly allocated to treatment with vindesine 3 mg/m2 combined with either epirubicin 40 mg/m2 or mitoxantrone 10 mg/m2. All drugs were given by intravenous push, treatment cycles were repeated at 3-4 week intervals. 255 patients were available for response, and 283 for toxicity. EV and MV yielded similar objective response rates (34 and 26%, respectively), response durations, times to progression and survival. Median time to remission was 1.8 and 3.1 months (P = 0.006) with EV and MV, respectively. In patients with visceral metastases, response rate was higher with EV than MV (40 versus 23%; P = 0.03). Patients receiving MV had less nausea/vomiting (P = 0.007) and alopecia (P = < 0.001) of WHO grade > or = 2. Bone marrow, cardiac and other toxicities were mild with both treatments. The observed differences in activity and toxicity between the two regimens appear to have clinical relevance. EV proved to be more active in visceral disease and to be able to induce remissions more rapidly. Accordingly, patients with visceral metastases or severe tumour-related symptoms may benefit from epirubicin-based treatment. Subjective toxicities, i.e. nausea/vomiting and alopecia, were less frequent and severe with MV. Thus, MV may prove useful in patients with more indolent disease and appears to warrant phase III evaluation in such patients.