The effect of hemodynamic shear stress on endothelial gene expression was investigated in the porcine iliac arteries. Computational fluid dynamics simulations identified three anatomical regions likely to experience high, medium, and low shear stress. The expression of genes in endothelial cells recovered from these regions were assessed using microarray. Keywords: shear stress, endothelial cell gene expression, in vivo Overall design: 11 iliac arteries were obtained from 6 animals, total RNA were extracted from high, medium and low shear region. The expression profiles were compared with a reference RNA using dual channel arrays. Samples with low original RNA quality and low hybridization quality were not included.