Neuropeptide Y (NPY), a 36-amino acid member of the pancreatic polypeptide family, was found to be present by immunohistochemistry in the bovine adenohypophysis. NPY mRNA expression was confirmed in the adenohypophysis by RT-PCR. NPY immunoreactivity was present in about 38% of adenohypophyseal cells in the pars distalis. However, NPY immunoreactive cells (NPY-ir cells) were scarce in the zona tuberalis. Immunohistochemistry of NPY and specific hormones using mirror sections revealed that NPY was colocalized in GH immunoreactive cells. Over 90% of somatotrophs corresponded to NPY-ir cells. These results indicate that endogenous NPY is present in the bovine somatotroph and may act as an endocrine intercellular mediator in the adenohypophysis.