CD34 and atherosclerosis: Atherosclerosis is regarded as a localized response to injuries of the endothelial cell layer triggered by factors such as smoking, high blood pressure, and hypercholesterolemia.1 Bone-marrow derived progenitor cells (PCs), circulating in the peripheral blood and detectable because they express CD34 on their cell surface, may play a role in repairing injured endothelium.2 A subset of these progenitor cells that express both CD34 and markers of endothelial lineage can home to sites of injury and differentiate into endothelial cells to help maintain the integrity of the endothelium.