Patients with leukocytoclastic vasculitis have purpuric, palpable lesions, most commonly on the lower part of the legs. Systemic involvement, particularly of the kidneys, is found frequently. Characteristic pathological features include necrosis of small vessels within the dermis, infiltration by polymorphonuclear leukocytes within and around the vessel walls, hemorrhage, and occasionally thrombosis. Immunofluorescence study frequently shows granular deposits of immunoglobulins and complement in vessel walls. Etiologic agents that have been implicated include infection, foreign proteins, chemicals, drugs, and a variety of diseases. The mechanism causing tissue damage is thought to be mediated by immune complexes, although specific antigens have only occasionally been unequivocally identified. Treatment includes bedrest, corticosteroids, and sometimes, cytotoxic agents.