Fabry disease, an X-linked systemic vasculopathy, is caused by a deficiency of alpha-galactosidase A resulting in globotriaosylceramide (Gb(3)) storage in cells. The pathogenic role of Gb(3) in the disease is not known. Based on previous work, we tested the hypothesis that accumulation of Gb(3) in the vascular endothelium of Fabry disease is associated with increased production of reactive oxygen species (ROS) and increased expression of cell adhesion molecules. Gb(3)-loading resulted in increased intracellular ROS production in cultured vascular endothelial cells in a dose-dependent manner. Increased Gb(3) also induced expression of intercellular adhesion molecule-1, vascular cell adhesion molecule-1, and E-selectin. Reduction of endogenous Gb(3) by treatment of the cells with an inhibitor of glycosphingolipid synthase or alpha-galactosidase A led to decreased expression of adhesion molecules. Plasma from Fabry patients significantly increased ROS generation in endothelial cells when compared with plasma from non-Fabry controls. This effect was not influenced by reduction of intracellular Gb(3). This study provided direct evidence that excess intracellular Gb(3) induces oxidative stress and up-regulates the expression of cellular adhesion molecules in vascular endothelial cells. In addition, other factors in patient's plasma may also contribute to oxidative stress in Fabry vascular endothelial cells.