Because vascular endothelial cell inflammation is critical in the development of cardiovascular pathology, we hypothesized that direct exposure of human aortic endothelial cells (HAECs) to ultrafine particles induces an inflammatory response. To test the hypothesis, we incubated HAECs for 4 h with different concentrations (0.001-50 microg/ml) of CeO(2) nanoparticles and subsequently measured mRNA levels of the three inflammatory markers intercellular adhesion molecule 1 (ICAM-1), interleukin (IL)-8, and monocyte chemotactic protein (MCP-1) using real-time polymerase chain reaction (PCR). Ceria nanoparticles caused very little inflammatory response in HAECs, even at the highest dose. This material is apparently rather benign in comparison with Y(2)O(3) and ZnO nanoparticles that we have studied previously. These results suggest that inflammation in HAECs following acute exposure to metal oxide nanoparticles depends strongly on particle composition.