In this experiment Toll-like receptor expression pattern in monocytes and monocyte-derived macrophages by lipopolysaccharide (LPS) stimulation was examined. Jugular venous blood was collected from four Japanese calves, and the peripheral blood mononuclear cells (PBMCs) were isolated. The cells were directly used for collecting monocytes by magnetic cell sorting or cultured for 7 days to collect monocyte-derived macrophages in Repcell. Then we analyzed the mRNA expression pattern of TLRs and cytokines in monocytes and monocyte-derived macrophages after LPS stimulation for 24 h. LPS stimulation of both monocytes and monocyte-derived macrophages resulted in an increase in the levels of mRNA transcripts for TNF-α, IL-6 and IL-8. Moreover, TNF-α and IL-6 mRNA expressions were significantly augmented by LPS stimulation in monocyte-derived macrophages.TLRs mRNA expressions were unchanged after LPS stimulation of monocytes, while TLRs mRNA expressions in monocyte-derived macrophages were complicated. TLR1, 3, 5, 8 and 10 were significantly decreased after LPS stimulation and there were no differences in the mRNA expressions of TLR2, 4, 6 and 7 between the groups of control and LPS stimulation. Besides, no expression of TLR9 was found. As antigen presenting cells, monocytes and monocyte-derived macrophages respond differently to LPS, so they may have different functions in the innate immune system. Cellular & Molecular Immunology. 2009;6(3):223-229.