An immunohistochemical study of the bovine pineal gland was performed by using polyclonal rabbit antisera raised against synthetic peptide fragments corresponding to the amino acid sequences of somatostatin-14, somatostatin-28, somatostatin-28<sub>1–12</sub>, and prosomatostatin<sub>20–36</sub>. Immunoreactive nerve fibers were demonstrated in the pineal gland with all four antisera. The nerve fibers were located throughout the gland, both perivascularly and intraparenchymally, with the highest density of fibers in the proximal part, close to the pineal stalk. A number of immunoreactive nerve fibers were also found in the habenular area and stria medullaris projections. Some of the fibers in the stria medullaris projections could be followed into the pineal gland via the rostral part of the pineal stalk. A few immunoreactive nerve fibers were present in posterior commissure, in the subcommissural organ and pretectal area. Thus, the present study shows that the bovine pineal gland is innervated by nerve fibers containing all four sequences of prosomatostatin. The anatomical location of the somatostatin-immunoreactive nerve fibers in the bovine pineal gland indicates that the perikarya of some of these nerve fibers are located in the brain.