It has been reported that chronic inflammation of the vessel wall is a hallmark of atherosclerosis. Interleukin-6 (IL-6) is regarded as an important modulator of inflammatory events occurring during all stages of atherogenesis. Although many factors that induce IL-6 expression have been identified, the effect of homocysteine (Hcy) on the expression of IL-6 in atherogenesis and the underlying mechanisms are not entirely clear. The objective of the present study was to investigate the role of Hcy in IL-6 expression in rat aorta vascular smooth muscle cells (VSMCs). After VSMCs were incubated with Hcy for various time periods, enzyme-linked immunosorbent assay (ELISA) and semi-quantitative reverse-transcriptase polymerase chain reaction (RT-PCR) were performed to measure the expression of IL-6. Electrophoretic mobility shift assay (EMSA) was used to examine nuclear factor kappaB (NF-kappaB) activity. Hcy (0.01-0.25 mmol/l) significantly increased the expression of IL-6 mRNA and protein in rat VSMCs. The increase in IL-6 expression was associated with the activation of NF-kappaB. Pyrrolidine dithiocarbamate (PDTC) suppressed Hcy-induced IL-6 release, a finding compatible with involvement of reactive oxygen species as second messengers in cytokine production mediated by Hcy. The present study has clearly demonstrated the ability of Hcy to elicit an inflammatory response in rat VSMCs by stimulation of IL-6 production and activation of NF-kappaB. Inflammation activation on vessel walls by elevation of Hcy may contribute to the pathogenesis of atherosclerosis.