Using a newly generated monoclonal antibody (2E6) against human B7-H3, we explored the expression of the molecule on dendritic cells derived from monocytes (Mo-DCs). Its expression was examined by means of immunostaining and flow cytometric (FCM) analysis. The results showed that B7-H3 was expressed in the course of Mo-DC maturation induced with interleukin 4 (IL-4) and granulocyte/macrophage colony-stimulating factor (GM-CSF). The expression could be detected at all the stages of Mo-DC differentiation, and remained at a quite stable level. Interestingly, B7-H3 was not expressed by T cells and B cells, even these cells were activated respectively by PHA or PWM. A weak expression could be detected on resting monocytes. These data showed that constitutive expression of B7-H3 at a high level was found on imDCs and mDCs derived from monocytes. Due to no expression on T cells and B cells, we speculate that B7-H3 might be another valuable molecule marker for Mo-DCs.