The dura mater has been implicated as a tissue where vascular headache develops. Identification of the neural components of this tissue is a prerequisite for understanding the mechanisms of this pathological process. The nitric oxide molecule, a potent vasodilator, may contribute to the vascular headache process by dilating dural vasculature. Our immunohistochemical study using nitric oxide synthase (NOS) antibodies revealed NOS-positive nerve fibers and a prominent mast cell population in the rat dura. A majority of the immunopositive fibers were associated with the anterior meningeal artery and its branches and sparse innervation with the middle meningeal artery, its branches, and superior sagittal sinus. We propose that the NOS-positive nerve fibers and mast cells be considered as possible participants in the pathogenesis of vascular headache.