Objcetives To sparch for the change of cerebrospinal fluid ferritin (CSF-Ft) content and its clinical significance.Methods The 42 patients with acute lymphatic leukemia(ALL)diagnosed by bone marrow biopsy were divided into 3 groups. There were 14 cases in Ⅰ group [introduced therapy stage without central nervous system leukemia(CNSL)7, 24 cases in Ⅱgroup (complete remission stage without CNSL) and 18 cases in Ⅲ grotip (with CNSL). There were 17 patients with viral encephalitis in viral encephalitis group and 15 patients without central nervous system oisease in control group. The CSF-Ft and SFt were determined by radioimmunoassay.Results The CSF-Ft contents of Ⅰ、Ⅱ、Ⅲ 、viral encepbalitis and control groups are 7.03 ?2.21 ?g/L,6.75 ?1.94?g/L, 31.06 ? 8.85?g/L, 7.26?1.83?g/L and 6.52 ?1.57?g/L. The CSF-Ft content in Ⅲ group are bigher than that in the other group (P