The hallmark of developing inflammatory lesions is the excess migration of recruited phagocytes together with the enhanced cell surface expression of adhesion molecules. Recent investigations give evidence that the two myeloid-related proteins MRP8 (S100A8) and MRP14 (S100A9), which are abundant in activated or recruited phagocytes, may have a modulatory role in inflammatory responses. S100A9 displays a regulatory role in the transendothelial migration of human monocytes, and the secreted S100A8/A9 complex may serve as a transport protein to move arachidonic acid to its target cells.