Rat sciatic nerve was observed by electron microscopy using the horseradish peroxidase (HRP) method. The nerve was crushed with a needle and HRP was injected around a sciatic nerve. After 5 hours to 3days, the nerve and spinal cord were dissected and observed under an electron microscope. Five hours after the injection, HRP granules were identified in the axoplasm of myelinated nerve fibers at the injection site. Many HRP granules were distributed in the cytoplasm of motor neurous of the spinal cord 3 days after the injection of HRP. There was no change in cell organella. The neurons in the spinal ganglia also did not show any ultrastructual changes in cell organella 2 to 3 days after the injection of HRP and had many HRP granules in their cytoplasm. These results showed that HRP injected into the crushed end of a sciatic nerve did not induce morphological changes in the motor neurons of the spinal cord and, sensory neurons in spinal ganglia.