The objective response rates were determined using teniposide as first-line chemotherapy for patients with recurrent breast cancer. Twenty-seven evaluable patients with advanced disease received teniposide 70 mg/m2 i.v. days 1-5 every 3 weeks. A total of 211 courses were given. Responses included one complete (4%) and 9 partial responses (33%) with a median duration of response of 9 months (range 2-31 months). The main toxicity was myelosuppression. The results show that teniposide has at least modest activity in patients with advanced breast cancer treated previously with endocrine therapy.