Activation of the vascular endothelium by several different stimuli plays a crucial role in the initiation, localization, and propagation of vascular injury. In vitro studies have demonstrated that activation of cultured vascular endothelial cells renders them hyperadhesive for leukocytes. During the past decade it has become evident which cell adhesion molecules play a critical role in the interaction between the vascular endothelium and leukocytes in inflammation in general. Over the past year, advances have been made in understanding the interactions between leukocytes and vascular endothelial cells in vasculitis. Several studies have shown increased expression of adhesion molecules on circulating leukocytes and, in situ, in vasculitic lesions. Soluble adhesion molecules have appeared to be general nonspecific markers of endothelial activation. Hence, the clinical relevance of measuring soluble adhesion molecules is limited. Finally, the possibility of inhibiting adhesion molecule function in vivo remains an attractive therapeutic option in the vasculitides and is a focus of increasing research activity.