Experiences in 13 children treated with radiocolloids (198Au and 32P) applied intrathecally are presented. This treatment may replace the external radiation therapy in prophylaxis or therapy of central nervous system (CNS) involvement in childhood leukemia and non Hodgkin lymphoma. The follow-up median value was 18 months. Ten children were treated for prophylactic aim. Two out of 10 presented meningeal failure 1 month after. Three patients treated for meningosis died for bone marrow relapse without evidence of blasts in CSF sediment.