Patients with acute lymphocytic leukemia (ALL) receive intrathecal methotrexate at the beginning of the study. If CNS involvement is documented, patients receive a second dose of methotrexate 48 hours later followed by oral leucovorin calcium every 6 hours for 4 doses. Patients with ALL and/or CNS involvement receive intrathecal methotrexate every other week for 12 weeks after transplant.