The homocysteine (Hcy)-induced tissue factor (TF) expression in human vascular smooth muscle cells (VSMCs) and the effect of Hcy on the activity of nuclear factor-kappaB (NF-kappaB) and the expression of inducible nitric oxide synthase (iNOS) were investigated. Human umbilical artery VSMCs were cultured by tissue explanting method, identified by alpha-actin immunohistochemistry, and incubated with different concentrations of Hcy/PTDC (NF-kappaB inhibitor). Semi-quantitative RT-PCR was performed to detect the expression of TF mRNA in VSMCs. Flow cytometry was used to assay the expression of TF protein on the surface of VSMCs and the expression of iNOS in VSMCs. Western blot was carried out to detect the expression of NF-kappaB protein in nuclei. The results showed that Hcy could induce VSMCs expressing TF mRNA significantly after the VSMCs were incubated with Hcy at concentrations of 10, 100, 500 micromol/L respectively. There was low expression level of TF protein on the surface of the resting VSMCs and Hcy could also induce VSMCs expressing TF protein on the cell surface in different concentrations. Additionally, Hcy could rapidly induce the activation of NF-kappaB and this effect could be significantly inhibited by PDTC. Hcy alone could not induce the expression of iNOS in VSMCs. It was concluded that Hcy could significantly induce the expression of TF in VSMCs and enhance the activation of NF-kappaB, subsequently mediate TF gene expression and protein synthesis. NF-kappaB-mediated expression of TF in VSMCs might be the important mechanism of atherosclerosis and thrombosis induced by Hcy.