Pathological studies were carried out of Guillain-Barré syndrome (GBS) and 13 rabbits with experimental allergic neuritis. It was shown that the postmortem pathological findings in the patients, who died at different stages of GBS, varied in the degree of axon degeneration, the amount of plasmocyte infiltration, the appearance of phagocytes and the proliferation of Schwann cells and fibroblast. But in all the cases in this series segmental demyelination of the peripheral nerve with lymphocyte infiltration occurred without exception. In the rabbits with EAN, it was found that there were small foci of demyelination in the cerebral white matter and diffuse hemorrhage in the grey matter of the spinal cord. Lymphocyte infiltration in the EAN rabbit group was seen in a much more extensive manner than that found in cases of the patients with GBS, but the proliferation of Schwann cells and fibroblast seemed to take place more slowly in comparison with the similar process as was revealed in the patients who died from GBS.