Objective
To investigate the muscle fiber conduction velocity and histopathologic changes in skeletal muscle after 7% phenol solutions intramuscular injection.

Method
Forty-five Sprague Dawley rats were divided into two groups: Experimental group, 30; Control group, 15. Experimental and control groups were injected with 0.1 cc of 7% phenol solution and 0.9% saline in right gastrocnemius, respectively. The histopathologic findings and muscle fiber conduction velocity were evaluated at 0, 1, 5, 14, and 28 days after each injection.

Results
In the light microscopic examination of experimental groups, vacuolar change, atrophy of myofibers, and intermyofiber cell proliferation were shown. The expression of synaptophysin began to be seen at 5 days and S-100 protein was increased 14 days after injection. In the electron microscopic examination of experimental groups, vacuolar change and denuded postsynaptic membrane were shown. In muscle fiber conduction study of experimental groups, the mean velocity were significantly slowed at 1, 5, 14, and 28 days after injection than those of control groups (p＜0.05).

Conclusion
On the basis of histopathologic findings, it is presumed that the mechanisms of paralysis following intramuscular injection of 7% phenol solutions were both myogenic and neurogenic. The slowing of muscle fiber conduction velocity tended to be related with the histopathologic changes of skeletal muscles after intramuscular injection with 7% phenol solution.