Morphometric and immunocytochemical data obtained from nerve biopsies in six patients with necrotizing angiopathic neuropathy were compared with the data obtained in five control patients without neurologic disease. The density of myelinated fibers were greatly decreased in all patients (more than 55 p.cent), and reached 70 p.cent in four patients. The g myelination ratio was elevated in one patient, indicating demyelination. The number of fibers immunolabeled for the neurofilament (NF) light chain (L) was also decreased from 31 to 96 p.cent. Labeling for medium (M) and heavy (H) NF subunits was less affected. On the contrary, the number of fibers expressing beta-tubulin (TUB) increased by 38 to 141 p.cent and the ratio of the number of fibers expressing TUB and NFL (TUB/NFL) was increased 3 to 33-fold (p<0.05). We have previously reported similar, though less pronounced, anomalies in axonopathies of unknown cause. These results suggest that diverse etiologies may lead to the same type of lesions of the axon cytoskeleton.