L-Arginine is a conditionally essential amino acid for humans and plays an important role in the regulation of cardiovascular function and antioxidative defense. Previous studies have focused on the important role of L-arginine as a physiological precursor in the generation of nitric oxide and polyamines in endothelial cells (cells that line the interior surface of blood vessels). Because of the rapid development of high-throughput proteomics technology, there is now growing interest in studying roles for L-arginine in modulating endothelial-cell protein expression. Of particular interest, recent proteomics analysis has shown that treatment of coronary venular endothelial cells with a physiological level of L-arginine (e.g., 0.1 mM) increases expression of structural proteins (vimentin and tropomyosin) and cytochrome bc1 complex iii-chain A, while decreasing expression of stress-related proteins (PDZ domain containing-3), in these cells. These findings aid in elucidating the mechanisms responsible for the beneficial effect of physiological levels of L-arginine on the circulatory system.