Toxicity limits the use of anthracyclines in elderly sick patients and in heavily pretreated patients. Since the liposomal preparation of daunorubicin (DNR) (DaunoXome, or DNX) is expected to be less toxic than conventional DNR, we tested DNX combined with high-dose arabinosyl cytosine (HDAC) in 42 adult poor-risk acute leukemia patients. Thirty-one patients had acute non-lymphocytic leukemia (ANLL). Of these, 12 patients were newly diagnosed but were not eligible for standard induction treatment, 13 were in first relapse, and 6 were in second or subsequent relapse. Eleven patients had acute lymphocytic leukemia (ALL), in first (eight cases) or second (three cases) relapse. DNX was given i.v. in three doses of 80 or 100 mg/m(2) each (days 1-3) by a 60-min infusion in glucose 5%, followed by a 4-h infusion of HDAC 2 g/m(2) (days 1-5). Among 31 ANLL patients there were 16 (51%) complete remissions (CR), 5 deaths during induction, and 10 failures. Among 11 ALL patients there were 10 CRs and 1 failure. The response rate was not affected by the overexpression of MDR-related proteins (PgP, MRP-1, and LRP). Non-hemopoietic toxicity was negligible, with no intestinal toxicity and only one case of gram-negative bacteremia. We conclude that DNX, in combination with HDAC, is an effective treatment for poor-risk adult AL. Because of the low non-hematologic toxicity, it can be used to reinduce remission in poor-risk patients who are candidates for allogeneic bone marrow transplantation. The high CR rate observed in ALL requires confirmation.