Objectives: This proposal addresses the overall hypothesis that ambient fine particulate matter exerts cardiovascular health effects via alteration of endothelial homeostasis, through a mechanism mediated by oxidative stress. This project will use a controlled human inhalation exposure to diesel exhaust particulate (DEP) as a model to address the following objectives: 1) Determine whether exposure to inhaled DEP is associated with endothelial dysfunction in a concentration-related manner; 2) Determine whether exposure to inhaled DEP is associated with evidence of systemic oxidative stress; and 3) Determine whether antioxidant supplementation blunts the DEP effect on endothelial function.