Markers for systemic vasculitis may be useful in both assessment of disease activity and ascribing pathogenesis. Endo-thelial cell damage may be assessed by Factor VIII-related antigen and perhaps fibrinolysis (plasmin inhibitor/plasmin complex). Antibodies to endothelial cells potentially combine both assessment and pathogenesis. Complement fixing antibodies to endothelial cells, previously reported in systemic lupus erythematosus and Kawasaki syndrome, are also elevated in rheumatoid vasculitis. Their relationship to vascular endothelial cell antibodies, reported in a wide spectrum of systemic vasculitis, is not clear. A direct role for neutrophils in some forms of vasculitis is supported by the overlap of rheumatoid vasculitis with Sweet's syndrome, previously associated with both Behçet's and Crohn's syndrome. An indirect role of persistent neutrophil inflammation at mucosal surfaces is suggested by the vasculitis with antineutrophil cytoplasmic antibodies seen in cyctic fibrosis. In other cases, vasculitis may be triggered by direct viral infection such as cytomegalovirus. Experimental models may clarify the confusion. In the MRL mouse, vasculitis appears independent of the B-cell hyperacticity. Experimental models of uveitis also support a role for T cells in the induction of vasculitis.