The acute-phase reactant C-reactive protein (CRP) is an important risk factor for coronary heart disease. However, the possible effects of CRP on vascular cells are not known. We tested the effects of CRP on expression of adhesion molecules in both human umbilical vein and coronary artery endothelial cells. Expression of vascular cell adhesion molecule (VCAM-1), intercellular adhesion molecule (ICAM-1), and E-selectin was assessed by flow cytometry. Incubation with recombinant human CRP (10 microg/mL) for 24 hours induced an approximately 10-fold increase in expression of ICAM-1 and a significant expression of VCAM-1, whereas a 6-hour incubation induced significant E-selectin expression. Adhesion molecule induction was similar to that observed in endothelial cells activated with interleukin-1beta. In coronary artery endothelial cells, induction of ICAM-1 and VCAM-1 was already present at 5 microg/mL and reached a maximum at 50 microg/mL, at which point a substantial increase in expression of E-selectin was also evident. The CRP effect was dependent on presence of human serum in the culture medium, because no effect was seen in cells cultured with serum-free medium. In contrast, interleukin-1beta was able to induce adhesion molecule expression in the absence of human serum. CRP induces adhesion molecule expression in human endothelial cells in the presence of serum. These findings support the hypothesis that CRP may play a direct role in promoting the inflammatory component of atherosclerosis and present a potential target for the treatment of atherosclerosis.