Endothelial cell (EC) activation plays a key role in inflammation, thrombosis and organ rejection. Normally, EC are in a quiescent state in which their function is to prevent coagulation and thrombosis, and to participate in the regulation of leukocyte migration from the bloodstream into the tissue. Upon activation with cytokines or other stimuli, EC up-regulate a number of genes, including E-selectin (ELAM-1), intercellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1, interleukin (IL)-1, IL-8, tissue factor (TF), plasminogen activator inhibitor-1 (PAI-1), MCP-1 (monocyte chemoattractant protein-1) and endothelial cell inducible gene (ECI-6). Arachidonic acid (AA) is produced by several cell types, including EC, and acts on various cells. We report here that AA inhibits the up-regulation of some, but not all genes that are induced with EC activation in a dose-dependent manner. AA suppresses TNF-alpha, IL-1 alpha, LPS or PMA-induced E-selectin expression, as well as mRNA accumulation of E-selectin, ICAM-1 and IL-8 stimulated by TNF-alpha. The inhibition appears to be at the level of transcription. At the same time under the same conditions AA does not, repress mRNA accumulation for PAI-1, ECI-6, MCP-1 and VCAM-1. We suggest that the induced expression of AA with EC activation may result in a negative feedback loop regulating further activation.