We have studied immunocytochemically the distribution of CGRP-containing nerve fibers in the PCB poisoned rats introducing experimental periodontitis. The results obtained were as follows. In the PCB poisoned rats, some specimens obtained from periodontitis-affected sites showed a slight increase in both the intensity of nerve staining and the nerve sprouting. However, no discernible difference in the occurrence and the distribution of nerves has been demonstrated between the PCB poisoned rats and clinically healthy rats. Further studies are needed to confirm the effects of PCBs on the initiation and progression of periodontitis.