Seventy-eight patients with acute nonlymphoblastic leukemia in relapse were treated with high-dose cytosine arabinoside (3 g/m2 intravenously (IV) every 12 hours for 12 doses) alone, or with three days of anthracycline antibiotics (doxorubicin 20 mg/m2 or daunorubicin 30 mg/m2 IV daily) after completing the course of cytosine arabinoside. Consolidation and maintenance therapy was not given. When anthracyclines were added there was no increase in frequency or severity of nonhematologic toxicity including conjunctivitis, photophobia, dermatitis, cerebellar dysfunction, and gastrointestinal disturbance. All 78 patients achieved aplasia of the bone marrow. Five patients in each group died before bone marrow recovery. The use of anthracyclines did not prolong bone marrow recovery, with both groups demonstrating adequate granulocyte and platelet counts about four weeks after beginning treatment. Forty-one (53%) of the total 78 patients achieved a complete remission. In patients not clinically resistant to conventional-dose cytosine arabinoside, both regimens were equally effective inducing a complete remission (high-dose cytosine arabinoside alone, 12/19 [63%]; with anthracycline, 11/17 [65%], P = .270); in patients clinically resistant, the regimen including anthracycline was superior (15/27 [56%] v 3/15 [20%], P = .022). The duration of unmaintained response was similar (median, five months), but the longest remissions occurred when anthracyclines were used. Thus, high-dose cytosine arabinoside is effective in producing remissions in relapsed patients with acute nonlymphoblastic leukemia, and the addition of an anthracycline enhances this effect.