Patients receive 506U78 IV over 2 hours on days 1, 3, and 5. If residual leukemia/lymphoma is present on day 22, then patients receive a second course of 506U78. If day 22 marrow is hypocellular, then a repeat bone marrow biopsy should be obtained on day 29 to assess response. For day 22 or 29 marrow that is in complete response, patients receive 506U78 for two more courses on days 1, 3, and 5, administered every 21 days. Patients are followed every 3 month for 1 year, then every 6 months for a maximum of 10 years.