Patients undergo induction therapy consisting of etoposide IV and mitoxantrone IV on days 1-5. Patients then receive PSC-833 IV over 124 hours beginning on day 2. A second course is administered no sooner than 21 days from the start of the first course if the marrow is hypocellular after the first course. Patients with persistent disease after 2 induction courses are removed from the study. Patients receive a total of 3 courses of etoposide/mitoxantrone. Patients who achieve complete remission after 1 induction course receive 2 courses of etoposide/mitoxantrone with PSC-833 as consolidation, beginning within 4 weeks of attainment of complete remission. Patients who achieve complete remission after 2 induction courses receive 1 course of etoposide/mitoxantrone with PSC-833 as consolidation. Cohorts of 3-6 patients receive escalating doses of PSC-833 until the maximum tolerated dose is determined. Patients are followed every 6 months.