An immunohistochemical study of the bovine pineal gland was performed using rabbit polyclonal antibodies raised against neuropeptide Y (NPY) or against the C-terminal flanking peptide of proNPY (CPON). A large number of NPY/CPON-immunoreactive (IR) nerve fibers were demonstrated throughout bovine pineal gland. The IR-fibers were located in the capsule of the gland, usually piercing into the gland together with blood vessels. In the gland itself, the fibers were also located intraparenchymally between the pinealocytes. Within the rostral and caudal areas of the pineal stalk, NPY-IR fibers were also observed, and these fibers could be followed not only into the gland but also to the habenular and posterior commissures. The morphological localization of the NPY-IR nerve fibers in the bovine pineal gland indicate that the majority of fibers originate from the superior cervical ganglion. However, some fibers probably originate from the brain itself.