Cytomorphological findings in the cerebrospinal fluid (CSF) of two patiens suffering plasma cell leukemia and non Hodgkin's mixed cell lymphoma are reported. In the first were found inmature plasma cells, polynucleate giant cells with giant nucleoli and atypical mitoses. In the second one polynucleate giant cells with hypercromatic and polyfissured nuclei and atypical mitoses are prominent. It is emphasized the importance of the early cytomorphological CSF study in patients with myelo or lymphoproliferatíve diseases.