We performed allogeneic bone marrow transplantation (BMT) with an extended period of post-transplant intrathecal (IT) chemotherapy for five patients with acute lymphoblastic leukaemia and non-Hodgkin's lymphoma who had relapsed in the central nervous system either in the very early phase or more than twice. Post-transplant IT was scheduled for a total of 12 doses over 18 months. One patient was found to have subclinical leucoencephalopathy. Disease relapse occurred in one patient and the other patients remained in complete remission for 39–196 months post-BMT. The estimated event-free survival was 80 ± 17·9% (standard error).