Pathological alteration of peripheral nerves in the mutant Syrian hamster with hind-leg paralysis were examined under the electron microscope. The changes included alteration of axonal caliber and abnormal distribution of axoplasmic contents. In addition, changes at the inner loop: axonal interface were noted which included accumulation of filamentous and granular material in the axon, loss of the inner loop membrane, and discontinuity of the subjecent axonal membrane. Demyelination and onion bulb formation was seen in the older hamsters.