Nitric oxide and calcitonin gene-related peptide (CGRP) have been implicated in craniofacial pain including migraine headache, and CGRP induces face-grooming indicative of nocifensive behavior in animals. The aim of this study was to test whether systemic administration of nitroglycerin (NTG) influences the CGRP-induced behavior in awake rats and whether sumatriptan, a 5-HT1B/1D receptor agonist, can block the effects of NTG. CGRP was not significantly different from normal saline in inducing face-grooming behavior but NTG facilitated the effect of CGRP. Furthermore, sumatriptan was found to block the effect of NTG. These data suggest that facilitatory processes involving nitric oxide may be necessary for CGRP to play a role in some craniofacial pain conditions including possibly migraine headache.