Forty premenopausal patients with advanced breast cancer entered a prospective and randomized study in which high-dose medroxyprogesterone acetate (HD MAP) and oophorectomy (OPX) were compared. All the patients were first treated for advanced disease. Twenty-two patients received HD MAP (1,000 mg b.i.d. p.o.) and 18 patients received OPX. Complete remission (CR) was achieved in 2 (9%) in the HD MAP group and in 2 (11%) in the OPX group for a duration of 20-24 and 30-54 months respectively. Partial remission (PR) was achieved in 10 (45%) patients in the HD MAP group and in 4 (22%) patients in the OPX group for a median duration of 9 and 7 months respectively. The objective response rates (CR + PR) were 55% for the HD MAP group and 33% for the OPX group (p = 0.17). Ten patients who received OPX as first-line treatment received HD MAP when the disease progressed and were evaluable for response: PR was achieved in 6 patients (2 responders and 4 nonresponders to OPX) for a median duration of 5 months. Two out of 4 patients who received OPX at progression after objective response to HD MAP presented PR. HD MAP induced a significant decrease in pain intensity and, compared to OPX, a more frequent improvement was induced in performance status. No difference was observed between the two groups in terms of overall survival. This study shows that HD MAP is an active treatment in premenopausal patients with advanced breast cancer and that it can induce a response in some patients resistant to OPX.