Sixteen adult patients with refractory acute non-lymphoblastic leukemia (ANLL) underwent reinduction therapy with idarubicin (12 mg/m2) i.v. on days 1-3) followed by cytosine arabinoside (120 mg/m2 every 12 h on days 4-10). Patients achieving complete remission (CR) received consolidation and early intensification courses which included idarubicin at lower dosage. CR was reached after a single course in 70% of the patients treated at first relapse, and two of the five subjects previously resistant to daunorubicin-containing regimens responded to the idarubicin protocol. The median duration of CR was 11 months. Gastrointestinal side-effects were not important; mild and reversible ECG changes were noted whereas delayed cardiac toxicity was not observed despite previous treatment with daunorubicin. These encouraging results confirm the efficacy of idarubicin in treating acute leukemia and suggest it may have a major role in the treatment of relapsed and refractory patients with ANLL.