The existence of ascending medullary neuropeptide Y (NPY)-containing projection from the spinal trigeminal nucleus to the pontine peribrachial area has been demonstrated by a combination of immunohistochemical methods with surgical transections in the lower brainstem. An NPY immunopositive cluster of varicose fibers was detected in the spinal trigeminal and in the paratrigeminal nuclei. Numerous immunoreactive perikarya could also be visualized here after colchicine treatment. Transections destroying the lateral region of the medulla oblongata resulted in an accumulation of NPY immunoreactivity in several trigeminal neurons ipsilateral to the knife cut, but no such retrograde accumulation was seen in any neuronal perikarya anywhere else in the medulla oblongata.