Anatomical and clinical observations suggest that supratentorial vascular structures contain afferent projections from the trigeminal ganglia. To characterize this innervation, horseradish peroxidase (HRP) and HRP conjugated to wheat germ agglutinin were applied to the pial and dural arteries and sinuses of 33 cats. HRP was restricted to the site of interest by applying it dissolved in a viscous polymer, polyvinyl alcohol (PVA), to achieve slow release and minimize diffusion. The ganglia of cranial nerves V, VII, IX, and X and the superior cervical ganglia (SCGs) were examined bilaterally for the presence of retrogradely transported protein. Horseradish peroxidase applied to the proximal middle cerebral artery was located in cell bodies occupying the portion of the ipsilateral trigeminal ganglion corresponding to the ophthalmic division and throughout both SCGs. When the tracer was applied to the right anterior or posterior superior sagittal sinus, HRP-positive cells were present as above, predominantly in the ipsilateral trigeminal ganglia corresponding to the ophthalmic division and throughout both SCG. When applied to the right middle meningeal artery, HRP was observed within neurons of ipsilateral SCG and in the ophthalmic division of trigeminal ganglia; a few enzyme-containing cells were present in ipsilateral regions corresponding to the second and third divisions. These observations support the concept that supratentorial vascular structures receive afferent nervous projections from trigeminal neurons.