Dendritic cells (DCs) are potent antigen-presenting cells and generated from diverse sources including monocytes which are known to be the sites for human cytomegalovirus (HCMV) latency. HCMV has been known to suppress or evade from immune functions involving monocytes and DC. Thus, it was attempted to investigate the effect of HCMV infection on the differentiation of DCs from monocytes. Monocytes were prepared from peripheral blood mononuclear cells and they expressed high levels of CD14, CD11a, CD11b, CD11c and HLA molecules, while they did not express lymphocyte-specific CD molecules. The surface expressions of CD molecules and HLA in immature DCs (imDCs) differentiated from HCMV-infected monocytes differed from those in unifected imDCs. Specifically, the expressions of CD11a, CD11b, CD11c, CD40 and HLA-DR were decreased compared to uninfected imDCs, while CD80 expression was increased in imDCs differentiated from HCMV-infected monocytes. DCs were allowed to mature (mDCs) by treating imDCs with interferon gamma and LPS. When HCMV-infected imDCs were differentiated to mDCs, the expression of mDC-specific CD83 as well as HLA molecules were decreased. Thus, our results suggest that HCMV inhibits phenotytpic differentiation of DCs.