A new formulation of megestrol acetate, a semisynthetic oral progestin used in the hormonal treatment of breast cancer, allows the administration of 160 mg of the drug in a single daily dose. Sixty-nine postmenopausal patients with advanced breast cancer have been treated with this regimen: five patients received megestrol acetate as first-line treatment of their metastatic disease, while all the others had been previously treated with one or more regimens of chemotherapy and/or hormone therapy. The median duration of the treatment for evaluable patients was 3 months (range 1-13+). Among 65 evaluable patients 2 complete responses and 12 partial responses (objective response rate 21.5%; 95% confidence limits 12.31%-33.49%) were observed. Median duration of response was 7 months (range 2-12+). Responses were observed both in visceral and in non-visceral sites of disease. Twenty-nine patients obtained a stabilization of disease (44.7%), and twenty-two progressed (33.8%). Median duration of stabilization was 4 months (range 3-13+). Median survival for all patients from the start of megestrol acetate was 9 months (range 1-22+). The most common side effect of therapy was weight gain, occurring in 36% of patients. Megestrol acetate on a single-daily-dose schedule can be considered as an interesting hormonal treatment for advanced breast cancer, especially in the clinical instance of patients who, after having obtained a remission or stabilization of disease with tamoxifen, need further palliative treatment.