Circulating immune complexes are thought to play an essential part in the pathogenesis of necrosing angiitis. This theory also allows a role to be attributed to certain infectious agents (viral, bacterial, parasitic) in the development of periarteritis nodosa (PAN). An infectious syndrome was found in all our 9 patients, aged 26 to 69 years, with histologically confirmed PAN: previous infection (over 15 days before hospital admission): otitis, hepatitis B, tonsillitis, ascaris (Case n.7), pulmonary tuberculosis, brucellosis, seropositivity for Chlamydia trachomatis (Case n.9), paratyphoid (Case n.5), seropositivity for Yersiniosis pseudo-tuberculosis (Case n.2), seropositivity for Chlamydia trachomatis (Cases 3 and 4), seropositivity for toxoplasmosis (Cases 4 and 6), seropositivity for rubella (Case n.8). Recent infection (less than 15 days before hospital admission): staphylococcus aureus septicaemia (Case n.1); Group A betahemolytic streptococcal urinary infection (Case n.2); Group A betahemolytic streptococcal otitis media; pseudomonas aeruginosa and Klebsiella septicaemia; enterococcal cystitis (Case n.4); progressive pulmonary tuberculosis (Case n.6), acinetobacter pneumonia (Case n.9). The HBs antigen was only found in one patient (Case n.6), who had an active hepatitis.