The new anthracycline-analogue 4-demethoxydaunorubicin (4-DMDR) was administered orally at the dose of 15 mg/m2 daily for three consecutive days and repeated every 21-28 days on 29 patients with advanced pretreated breast cancer. A partial remission was observed in 7/25 evaluable patients (28%) for a median duration of 7 months. Side-effects include leukopenia in 93% of the patients (less than 1000 WBC/mm3 in 7%), nausea in 41%, mild vomiting in 17%, diarrhea in 10% and alopecia in 10% of the patients. No definitive conclusion is possible regarding cardiotoxicity. Only mild changes in ECG were observed in two patients. This study shows that 4-DMDR administered orally is well tolerated in the majority of patients and has antitumor activity in advanced breast cancer.