[Polyarteritis Nodosa].

With reference to sixteen cases of polyarteritis nodosa (seven dogs, two cats, two goats, three pigs, two cattle), current views regarding classification, aetiology and pathogenesis of this disease are discussed. Polyartertis nodosa is not a disease entity, but rather a symptom that may be associated with various forms of disease and may vary in pathogenesis. The clinical picture depends upon the localisation of the vasculitis. Toxic agents and various viruses may be directly responsible for the vascular lesions. In addition, genetic, autoimmune and allergic factors may be implicated. The immunological pathogenesis is illustrated with reference to the serum sickness model.