We investigated the effect of antiretroviral therapy on vascular activation in 41 human immunodeficiency (HIV)--infected patients receiving a regimen that included either at least 1 protease inhibitor (PI; n = 21) or a nonnucleoside reverse-transcriptase inhibitor (NNRTI; n = 20). A control group of 21 healthy subjects was included for comparison. Levels of endothelial markers (soluble vascular cell adhesion molecule [sVCAM]--1, soluble intercellular adhesion molecule--1, and von Willebrand factor) were higher in HIV-infected persons before treatment than in control subjects and decreased significantly after 5--13 months of treatment. Levels of sVCAM-1 and von Willebrand factor correlated significantly with initial virus load. d-dimer concentrations also decreased significantly after initiation of treatment. PI- and NNRTI-containing regimens had similar effects. Therapy did not reduce levels of the soluble platelet (sP) activation markers sP-selectin and CD40 ligand. The inhibition of markers of vascular activation may counterbalance sequelae of therapy-induced dyslipidemia and potentially prevent development of atherosclerosis in HIV-infected patients.