The results of two different methods of CNS prophylaxis during consolidation were evaluated among fifty one acute lymphoblastic leukemia patients (ALL) treated in 1980-1991 in the Department of Hematology in Katowice. In group I (n = 28) methotrexate (Mtx) was used intrathecally (it) in 6 doses of 18 mg, in group II high dose cytosine arabinoside (Hi AraC)--3g/m2 intravenously (4x) was used with CNS rtg--therapy (18-24Gy). In both groups frequency of CNS relapses was similar 17.8% vs 17.3%; additionally there were no statistically significant differences in RFS: 369 vs. 562 days. The survival of patients with and without CNS relapses was also similar (678 vs. 774 days) and was independent of prophylaxis. The tolerance of both the used methods of CNS prophylaxis was good.