Lesions of vasculitis of nerve were found in 33 of 140 patients hospitalized for peripheral neuropathy over a little less than 2 years, and in 113 specimens from neuromuscular biopsies. A first group of 7 patients had histological lesions suggestive of systemic necrotizing vasculitis (periarteritis nodosa in 4 cases and Churg and Strauss disease in 2 cases); the 7th patient was treated for myeloproliferative syndrome. The clinical and electromyographic signs were those of an axonal polyneuropathy which was improved by various treatments in 6 cases. A second group of 26 patients had histological lesions of vasculitis of nerve. Ten of these patients presented with single or multiple neuritis (of unknown origin in 5 cases), 11 with distal polyneuropathy (of unknown origin in 5 cases) and 3 with chronic polyradiculoneuritis; in 2 cases, clinical and electromyographic findings were in favour of an anterior horn lesion. The duration of the disease varied from 6 months to 10 years. The principal causes identified were connective tissue diseases, solid cancer or lymphoma and isolated gammapathy. Two patients with multiple neuritis recovered spontaneously. The finding of vasculitis of nerve at biopsy therefore is of unequivocal significance outside the better known but smaller group of systemic necrotizing vasculitis.