One of the most encouraging endeavors in pediatric oncology in recent years has been the development of treatment regimens for acute lymphoblastic leukemia. Remission in children with leukemia was first induced with aminopterin in 1948(1). Since then, other drugs have been used in numerous combinations. Prior to the late 1960's, when effective prophylactic treatment for central nervous system leukemia was developed, a child with leukemia who successfully maintained bone marrow remission had a 40 to 50 percent chance of developing meningeal leukemia as a complication of his illness. Leukemia in the central nervous system is frequently followed by recurrence of disease in bone marrow(2). The central nervous system apparently is shielded from systemic chemotherapy by a physiologic barrier termed "the blood-brain barrier."