Monoclonal antibody and recombinant DNA technologies have led to the development of biologic therapies capable of directly targeting selected components of the immune response. With the steady expansion of knowledge regarding the mechanisms of vascular inflammation, the safety and efficacy of biologic agents in the vasculitic diseases are being increasingly investigated. By targeting specific effector mechanisms involved in the pathogenesis of vasculitis, these agents may provide a less toxic means of inducing remission and lessening relapse. However, the study of biologic therapies in the vasculitides must be approached with caution, as unanticipated effects on disease activity and disease-specific toxicities can occur. Studies to examine these agents must recognize the potential for active vasculitis to be organ- or life-threatening as well as the current existence of effective therapies. In the research setting, investigation of biologic agents in the treatment of vasculitic diseases may also provide important insights into pathogenesis of these syndromes.