Twenty patients (pts) with metastatic breast cancer with disease progression, previously treated with chemotherapy and tamoxifen, were administered oral letrozole (2.5 mg/day) therapy. Fifteen of the patients were postmenopausal and 5 were premenopausal. Ten were estrogen receptor (ER)-positive, 7 were unknown and 3 were ER-negative. All the patients were assessed after 6 months (mo) of chemotherapy. Nine pts (45%) presented a partial response (PR), five (25%) had a stable disease (SD) and six (30%) had a progressive disease (PD). In the pts with PD, six out of 15 (33%) obtained a PR while undergoing tamoxifen therapy. The treatment caused no significant toxicity.