We have reviewed the clinical and morphological data from 100 patients with necrotizing arteritis in muscle and/or in nerve samples taken by biopsy. The neuropathy occurred in the context of a multisystem disorder (Group 1) or in apparent isolation (Group 2). The average age of patients was 59 in Group 1 and 61 in Group 2. Females were more commonly affected than males, especially in the first group. Necrotizing arteritis complicated the course of rheumatoid arthritis in 25 patients. In 3 patients necrotizing arteritis was associated with infection with the human immunodeficiency virus, the agent of AIDS. Tests for hepatitis B surface antigen were positive in 19 patients. Mononeuritis was present in 13, mononeuritis multiplex in 62, and distal symmetrical sensory or sensorimotor neuropathy in 19 patients. In both groups of patients, the muscle biopsy was more frequently diagnostic for arteritis than was the nerve biopsy (80% versus 55%). The average incidence of isolated fibers undergoing axonal degeneration was 64.8%; that of demyelinated/remyelinated fibers was 1.9%. We conclude that the combination of nerve and muscle sampling increases the chance of visualizing characteristic arterial lesions in vasculitic neuropathy.