Abstract： Objective To investigate the levels of IL-18 in the bone marrow of both normal subjects a nd patients with hematological diseases and to determine the possible significan ce of IL-18 in pathogenesis of some hematological malignancies. Methods The IL-18 mRNA levels in the bone marrow of 140 patients with hematological dis eases and 15 normal donors were determined by the semi-quantitative reverse tra nscriptase polymerase chain reaction (RT-PCR). Immunohistochemical method was used to detect IL-18 protein in 12 patients with acute myeloid leukemia (AML). The possible regulation of IL-18 for proliferation of some leukemia cells was investigated using antisense techniques.Results IL-18 mRNA levels were obviously higher in the patients with leukemia or other malignant hematological diseases (OMHD) than in normal donors. However, no sign ificant difference was found in the level of transcription between patients with iron deficiency anemia (IDA) and normal controls. Immunohistochemical method c onfirmed the presence of IL-18 protein in 10 out of 12 AML cases with positive transcription. By 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium b romide (MTT) assay, IL-18 antisense oligodeoxynucleotides (ASON) clearly inhibi ted the growth of J6-1 and HL-60 cells (42% and 12% inhibited, respectively) i n a dose-dependant manner.Conclusions IL-18 was detected at elevated levels in the bone marrow of patients with some hematological malignancies, and might be involved in the proliferation of certai n leukemic cells in vivo through an autocrine mechanism.