The responsibility of bacterial agents in the staring of systemic vasculitis is discussed on the basis of four cases: three men and one woman presenting with severe vasculitis which revealed or complicated a focus of infection without hematogenic dissemination. Two patients had gastrointestinal lesions and one had severe renal lesions. The vasculitis affected small caliber vessels, and in two out of four cases it involved arterioles of medium caliber with histological images resembling periarteritis nodosa. Antibiotic therapy alone was immediately effective against vasculitis. However, a purely cutaneous relapse occurred in three patients whose disease had regressed under an adjuvant treatment.