The cases of four patients with lymphoma with leucemic conversion, who exhibitted neoplasic infiltration of the central nervous system and of the meninges are reported. The anatomo-pathologic study showed the presence of small nodules of leucemic cells, in two patients. The other two patients had clinical improvement after the use of metotrexate by spinal route so that the anatomo-pathologic study of their CNS and meninges showed no abnomality.