This protocol aims to assess endothelial function among a group of HIV-infected patients with varying degrees of viral activity and levels of immune function on a variety of HAART regimens. It also aims to evaluate the effect of three different medications on lipids, insulin resistance, and thus endothelial function. Understanding the factors involved in causing endothelial dysfunction will help better characterize the relative risks and benefits of early versus late and continuous versus intermittent HAART therapy. The research may offer some insights into the causes of premature heart disease among HIV-infected patients on HAART that could be more thoroughly investigated in subsequent clinical trials.