Seven hours after injection of 5 mg of horseradish peroxidase (HRP) dissolved in 10 microliter normal saline into the anterior chamber of the eye directly into the iris of rats, sympathetic ganglion cells projecting to these regions were detected by numerous HRP-positive granules in their cytoplasm. By light microscopy, these HRP-labelled granules appeared as heavy brown granules, ultrastructurally they were demonstrated in the vesicles and tubules of smooth endoplasmic reticulum and in the lysosome-like dense bodies in the perikaryon of the neuron. The HRP reaction product was also detected in the vesicles and tubules of smooth endoplasmic reticulum within the axons in the superior cervical ganglion. The neurons projecting to the iris dilator muscles, which showed an HRP-positive reaction were scattered in the ganglion, and the rate of retrograde axonal transport of HRP was 4 mm/hour. The present study revealed that the greatest amount of strong reaction product was found in the neurons from animals 2 days after injection of HRP, and that HRP-labelled ganglion cells also have the capacity for dendritic transport of HRP. The HRP reaction product that disappeared from ganglion cells by 7 days post-injection of HRP was probably due to the lysosomal degradation.