The pathological basis of nerve inexcitability in GuillainBarré syndrome has not been established with certainty. We report the clinicopathological findings in a 67-year-old patient with fulminant GuillainBarré syndrome who died 18 days after onset. Three serial electrophysiological studies revealed nerve inexcitability. Antibodies to Campylobacter jejuni were present but there was no antiganglioside reactivity. Spinal root sections revealed extensive and almost pure macrophage-associated demyelination with occasional presence of T lymphocytes and neutrophil leukocytes. Conversely, in femoral, median, and sural nerves the outstanding lesion was axonal degeneration, with some denuded axons remaining. Unmyelinated fibers, posterior root ganglia, and dorsal columns were preserved. Endoneurial postcapillary venules showed plump endothelial cells with loss of their tight junctions. We conclude that both primary demyelination and axonal degeneration secondary to inflammation account for nerve inexcitability. Our findings lend support to the hypothesis of increased endoneurial pressure as the cause of wallerian degeneration in nerve trunks. The Guillain-Barré syndrome (GBS) is an acute or subacute evolving paralytic disease of unestablished etiology with characteristic pathological features of macrophage and lymphocytic infiltration of peripheral nerve with myelin destruction. 2,3 Nerve conduction studies reveal the typical findings of an acute multifocal demyelinating polyradiculoneuropathy consisting of proximal or distal conduction block and slowing of conduction. 1,9,16,39,46,62 In a small proportion of GBS cases, however, one or more peripheral nerves are inexcitable. 1,62,72,73 Because of the scarcity of detailed autopsy studies, 5,[18][19][20]75 the pathological basis of nerve inexcitability in GBS is controversial, three explanations being possible: distal demyelination with conduction block, secondary wallerian degeneration following demyelination, or primary and severe axonopathy. 5,10,[18][19][20]49,72,73,75 Serial electrophysiological studies have shown that conduction block, the physiological hallmark of demyelination, often precedes the appearance of axonal degeneration. 72,73 Exceptionally inexcitable nerves may be an early and inaugural electrophysiologic feature which has been related to axonal degenera-