Many therapeutic agents, including recently introduced biologic response modifiers, can induce a variety of vasculitic manifestations ranging from small vessel hypersensitivity vasculitis and leukocytoclastic vasculitis to distinct vasculitic syndromes such as Wegener's granulomatosis, polyarteritis nodosa, and Churg Strauss syndrome. The pathogenic mechanisms remain to be defined and appear to be multifactorial, with cell-mediated and humural immune mechanisms playing important roles. Clinical presentation varies in severity from mild to severe and even fatal illness, can be self-limiting, or follows a more chronic protracted course. There are no significant differences in clinical presentation, serologic abnormalities, and pathologic findings with the idiopathic forms of vasculitis. However, it is extremely important to identify the offending drug because the discontinuation of the drug is often followed by a rapid improvement of the underlying vasculitic disorder.