Cytokines play an important role in inflammation and immunity. In this study, we examined the expression and presence of human macrophage migration inhibitory factor (MIF) in human myelomonocytic leukemia cell line, HL-60 by reverse transcription-polymerase chain reaction (RT-PCR) and immunological methods (Western blot analysis and immunohistochemistry), respectively. The RT-PCR showed that MIF mRNA was constitutively expressed, and the expression was further induced by lipopolysaccharide (LPS) stimulation. The expression was upregulated by LPS at the range of 10 pg/ml to 10 ng/ml; however, it decreased at doses higher than 100 ng/ml. The expression reached the maximum 12 hr after the stimulation, but substantially decreased by 24 hr. Western blot analysis and immunohistochemistry using an anti-human MIF antibody revealed the presence of MIF protein in cytoplasm of the cells. The pathophysiological role of MIF in HL-60 cells has not been fully understood; however, the regulation of MIF mRNA expression by LPS suggests the possibility that the cytokine plays an important role in inflammatory events of leukemia.