Lopinavir-ritonavir is one of the most commonly used antiretroviral therapy. It also produces lipid abnormalities. Thus, an important part of the investigating factors contributing to atherosclerosis would be to determine if this drug can adversely influence endothelial cells in the absence of HIV infection or low CD4 counts. This would suggest that this drug directly or indirectly could predispose to atherosclerosis. Endothelial function is an important contributor to atherosclerosis. Invasive and non-invasive methods to evaluate endothelial cell function have been validated as predictors of coronary artery disease. These techniques have been used at NIH for clinical investigation for many years.