Coronary artery disease (CAD) is the leading cause of death worldwide. It has been established that internal mammary arteries (IMA) are resistant to the development of atherosclerosis, whereas left anterior descending (LAD) coronary arteries are athero-prone. The contrasting properties of these two arteries provide an innovative strategy to identify the genes that play important roles in the development of atherosclerosis. We carried out microarray analysis to identify genes differentially expressed between IMA and LAD. Twenty-nine genes showed significant differences in their expression levels between IMA and LAD, which included the TES gene encoding Testin. The role of TES in the cardiovascular system is unknown. Here we show that TES is involved in endothelial cell (EC) functions relevant to atherosclerosis. Western blot analysis showed higher TES expression in IMA than in LAD. Reverse transcription polymerase chain reaction and western blot analyses showed that TES was consistently and markedly down-regulated by more than 6-fold at both mRNA and protein levels in patients with CAD compared with controls without CAD (P= 0.000049). The data suggest that reduced TES expression is associated with the development of CAD. Knockdown of TES expression by small-interfering RNA promoted oxidized-LDL-mediated monocyte adhesion to ECs, EC migration and the transendothelial migration of monocytes, while the over-expression of TES in ECs blunted these processes. These results demonstrate association between reduced TES expression and CAD, establish a novel role for TES in EC functions and raise the possibility that reduced TES expression increases susceptibility to the development of CAD.