 - Consolidation I SR patients: Patients receive vincristine IV and IT MTX on day 1 and oral mercaptopurine once daily on days 1-14. Patients also receive high-dose MTX HDM IV continuously over 24 hours on day 1 and leucovorin calcium IV every 6 hours beginning 36 hours after the start of the HDM infusion and continuing until MTX levels are undetectable. Patients proceed to CNS therapy after day 21. 