Background/Aims: The ability of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) to activate vascular endothelium is unclear. This study investigates the link between endothelial apoptosis and activation in response to TRAIL. Methods and Results: Endothelial cell apoptosis was modeled with the immortalized human endothelial cell line EA.hy926, and with primary human umbilical vein endothelial cells (HUVEC) sensitized with the phosphatidylinositol 3-kinase inhibitor LY294002 in 1% serum. EA.hy926 expressed greatest levels of TRAIL receptors R1 and R2, and HUVEC of R2 and R3, determined by flow cytometry. Recombinant human (rh)TRAIL induced apoptosis in both models, reducing cell numbers preventable with caspase inhibitors, and confirmed by annexin V staining. In EA.hy926, rhTRAIL activated NF-ĸB (1 h) with increased ICAM-1 expression (24 h). rhTRAIL also increased adhesion of human neutrophils, blocked with an antibody to neutrophil CD18, a ligand for ICAM-1, and with antibodies to TRAIL and TRAIL-R1 and R2. rhTRAIL increased neutrophil adhesion to sensitized HUVEC, without effect on unmodified HUVEC. rhTRAIL did not increase surface labeling of ICAM-1 or E-selectin in sensitized HUVEC. Conclusions: TRAIL increases neutrophil adhesion when it concurrently induces apoptosis both in EA.hy926 and in sensitized HUVEC. TRAIL may therefore induce endothelial activation in concert with endothelial apoptosis.