The affection of the sympathetic and parasympathetic structures of the peripheral nervous system in rabbits with experimental allergic neuritis (EAN) was demonstrated light- and electron-microscopically. The general characteristics of the microscopic findings were qualitatively similar to those previously established in the somatic nervous system, but they were less extensive. The neuronal perikarya and the axons in the autonomic nervous system (ANS) were mostly normal. Occasionally, cytoplasmic vacuoles in a few nodose ganglion neurons and some degenerating axons were seen. Other than myelin derived antigens could be operating in whole-nerve induced EAN, since inflammatory cells also infiltrated target tissue areas devoid of myelinated nerve fibers. The presence of numerous plasma cells in the target tissue suggests that local antibody formation may contribute to the destructive process. Our results establish that the ANS is frequently affected in EAN, especially in the more severe forms. Thus EAN was proved to be also in this respect a useful model for the human disease Guillain-Barré syndrome, which likewise is often complicated by autonomic dysfunctions.