The cytocentrifuge provides a satisfactory method to distinguish malignant from nonmalignant CSF mononuclear elements in leukemic patients with pleocytosis. In patients who have had meningeal leukemia, our data support the concept that absence of all blasts be required to define remission. The finding of rare blasts by cytocentrifuge in patients with prior history of CNS leukemia, however, should be interpreted in light of the entire clinical and laboratory picture.