By means of double staining technique of NADPH-diaphorase (NADPH-d) histochemistry and calcitonin gene-related peptide (CGRP) immunohistochemistry, we investigated the coexistence of NADPH-d reactivity and CGRP immunoreactivity in the canine superior cervical ganglion (SCG). Most of NADPH-d reactivity and CGRP immunoreactivity were coexisted in the principal postganglionic neurons. These neurons were distributed throughout the ganglion without specific localization. The present findings suggest the intimate role of CGRP and nitric oxide in postganglionic neurons of the canine SCG.