Mitoxantrone is a relatively new synthetic anthracenedione derivative with intercalating properties. An in vitro study with established leukemia cell lines indicated that DNA strand breaks were caused by mitoxantrone; when these were progressive after the initial insult, the cell line was sensitive to the drug. Clinical trials involved patients with relapsed and/or refractory acute leukemia. None of the patients receiving a single slow infusion of mitoxantrone achieved a complete remission. A five day treatment regimen produced an overall response rate of 48% with a complete remission rate of 25%. Toxicity in these preliminary studies was limited compared to that expected with the anthracycline antibiotics. Alopecia and nausea were the only commonly observed side effects. The trials were too short, however, to evaluate possible cardiac toxicity. Mitoxantrone is an acute and relatively nontoxic agent that merits further study to identify its role in the first line therapy of acute leukemia; such studies are underway.