Tissue factor (TF) is an important regulator and effector molecule of coagulation. It is primary known as a cofactor for factor VIIa-mediated triggering of blood coagulation, which proceeds in a cascade of extracellular reactions, ultimately resulting in thrombin formation. In sepsis, expression of TF by activated monocytes, macrophages and endothelial cells may lead to disseminated intravascular coagulation. Further studies have suggested that TF also plays non-haemostatic roles in blood vessel development, tumor angiogenesis, metastasis and inflammation. In the present study we examined the feasibility of inhibiting lipopolysaccharide (LPS)-induced TF expression in cultured human umbilical vein endothelial cells (HUVECs) using a modified phosphorothioate antisense oligodeoxynucleotide targeted to the TF mRNA. CD31 receptor-mediated endocytosis was used as a means of delivering TF antisense oligomer to HUVECs. This DNA carrier system consists of anti-CD31 antibody conjugated to the antisense. Co-exposure of HUVECs with TF antisense and LPS resulted in 54.6+/-3.2% suppression of TF activity when compared with control LPS stimulated cells. The antisense also reduced the LPS-induced TF mRNA level. Control experiments with TF sense and mismatched antisense oligomers were performed to exclude non-specific inhibitory effects. The cytotoxicity of the antisense oligomer conjugate was also evaluated. Results demonstrate that this TF antisense oligomer specifically suppressed the synthesis of biologically active endothelial TF and that antisense oligomers might represent a useful tool in the investigation of endothelial TF function/biology.