Recent evidence suggests that smooth muscle cells within the intima of diseased human blood vessels of the elderly population contain the embryonic form of smooth muscle cells. We wanted to explore the idea that human diseased vessels may contain other primitive cell types, such as pluripotent embryonic stem cells and hematopoietic stem cells. Radial and internal mammary arteries were collected from patients undergoing coronary artery bypass surgery; and coronary arteries, from hearts at autopsy and transplant. Immunohistochemistry was used to identify the embryonic stem cell markers Octomer-4; stage-specific embryonic antigens 1, 3, and 4; TRA-1-60; and TRA-1-81, and the leukocytic markers CD34, CD14, CD133, and CD64 in all vessels. We found that diseased human radial arteries contained the highest numbers of cells in the media- and intima-expressing markers of embryonic and leukocytic origin compared with diseased human coronary arteries. In nondiseased human vessels (internal mammary arteries), such cells were rarely observed. Granulation tissue within the diseased human arteries contained similar cells, and the angiogenic vessel endothelial cell layer also expressed these markers. It is concluded that diseased human blood vessels contain cells that express markers from leukocytic and embryonic origin. These results suggest that cells within human arteries might be able to differentiate into various cell types and that blood vessels might be a reservoir for such cells.