Atherosclerosis is an inflammatory disease. Platelet-endothelium interaction plays an important role in the pathophysiology of atherogenesis. We investigated the role of activated platelets for secretion of interleukin (IL)-1β, monocyte chemotactic protein (MCP)-1 and macrophage inflammatory protein (MIP)-1α and expression of intercellular adhesion molecule (ICAM)-1 on endothelial cells. Human umbilical vein endothelial cells (HUVEC) were incubated with non-stimulated or ADP-activated platelets for 6 hr. Secretion of interleukin (IL)-1β, MCP-1 and MIP-1α and surface expression of ICAM-1 were measured by ELISA and flow cytometry. In the presence of activated platelets, the secretion of IL-1β, MCP-1, and MIP-1α and surface expression of ICAM-1 were significantly increased compared with non-activated platelets. The present study shows that activated platelets may contribute to expression of various inflammatory mediators on endothelial cells.