1. Human exposure to inhaled DEP (at concentrations approximating 0, 100, 200 μg PM2.5/m3 [PM less than 2.5 microns in aerodynamic diameter]) results in concentration-related alteration of endothelial homeostasis, as reflected in ultrasonographic measurement of the brachial artery, plasma markers of endothelial homeostasis (endothelin-1, ICAM-1 [intercellular adhesion molecule-1], e-selectin, nitric oxide metabolites nitrate [NO3-] and nitrite [NO2-], IL-6, and TNF-α), and markers of thrombosis associated with endothelial activation or injury (plasminogen activator inhibitor-1 [PAI-1], Von Willebrand's factor [VWF], and D-dimer).