It is now recognized that endothelial cell injury is an important initiating event in atherogenesis. Endothelial injury and desquamation may be induced by either physical (e.g., hemodynamic injury) or biochemical induced injury (e.g., hypercholesterolemia, endotoxemia, or homocysteinemia). A project will be initiated to assess the potential of using flow cytometry (allows rapid measurement of fluorescence of stained single cells flowing in suspension) to quantify circulating endothelial cells as an index of vascular injury. Additionally, flow cytometry will be evaluated as a means of analyzing cell suspensions prepared from atheromatous lesions.