Immune complexes are involved in the pathogenesis of Henoch-Schönlein purpura, essential mixed cryoglobulinemia, hepatitis B-associated periarteritis nodosa and hypersensitivity vasculitis (related to infection or medications). ANCA's probably play a pathogenic role in Wegener's Granulomatosis, microscopic polyangiitis and renal-limited vasculitis. Pathologic responses of T-lymfocytes and granuloma formation have been demonstrated in temporal arteritis, Takayasu arteritis, Wegener's Granulomatosis, Chürg-Strauss syndrome and Kawasaki syndrome. The eventual pathogenic role of AECA's is less clear, with the possible exception of rheumatoid arthritis and systemic lupus erythematosus. These four pathogenic factors are not mutually exclusive: several mechanisms may play in one disorder, as has been demonstrated for Wegener's Granulomatosis. From these new insights in the pathogenesis of vasculitis, new therapies with better efficacy and fewer side effects may arise.