The pathogenesis of vasculitis is complex and involves a variety of mechanisms acting in concert to bring about necrotizing inflammation of blood vessel walls. In recent years, there has been considerable progress in dissecting the immunologic abnormalities present in specific vasculitis syndromes. The primary immunopathogenic events that initiate the process of vascular inflammation and blood vessel damage, however, are still largely unknown. Although the cause of most vasculitis syndromes remains a mystery, advances in molecular and cellular immunology have defined many of the effector mechanisms that mediate inflammatory vascular damage. In this regard, modulation of the inflammatory response by specific cytokine and adhesion molecule antagonists is now possible and may prove beneficial in the treatment of vasculitis.