During the development of atherosclerosis, the major cause of cardiovascular disease, the vascular wall becomes thickened and remodelled as a result of the formation of atherosclerotic plaques. This results in a hypoxic environment as a result of a limited diffusion and increased demand for O2. Increasing evidence suggests that hypoxia is a driver of the modifications of extracellular matrix (ECM) in the artery wall during atherosclerotic lesion development. These changes may result in mechanical instability and an increased risk of atherosclerotic lesion rupture, which ultimately results in myocardial infarction or stroke. Aims: To investigate whether there is an altered composition of the ECM generated by human coronary artery endothelial cells (HCAEC) cultured under 1% compared to 20% O2 and whether any ECM changes modulate HCAEC adhesion, proliferation, gene expression of inflammatory cytokines, and generation of reactive oxidants. Results: Changes in mRNA expression, and antibody recognition of ECM components, were observed in response to HCAEC exposure to 1% O2 for 7 days. Marked increases were detected in the expression of the ECM proteoglycan versican. Decreased mRNA expression of cell adhesion molecule, ICAM-1, the inflammatory cytokines TNF-α and TGF-β, and increased oxidant generation were also detected. Consistent with decreased ICAM-1 expression, reduced adhesion of HCAECs to native ECM (generated under 1% O2) was also observed. In contrast, cellular metabolic activity (as measured by the MTS assay) was increased. Conclusion: These data indicate that 1% when compared to 20% O2 alters the ECM generated by endothelial cells. The increased production of versican may exacerbate the progression of atherosclerosis, as this proteoglycan is a well-established binding site for lipoproteins, and hence may contribute to lipoprotein retention in lesions. The concurrent increase in oxidant production may exacerbate lipoprotein modification, and the accumulation of lipid-laden cells in developing atherosclerotic lesions